A thesaurus (pl.: thesauri or thesauruses), sometimes called a synonym dictionary or dictionary of synonyms, is a reference work which arranges words by their meanings (or in simpler terms, a book where one can find different words with similar meanings to other words),[1][2] sometimes as a hierarchy of broader and narrower terms, sometimes simply as lists of synonyms and antonyms. They are often used by writers to help find the best word to express an idea:

...to find the word, or words, by which [an] idea may be most fitly and aptly expressed

Synonym dictionaries have a long history. The word 'thesaurus' was used in 1852 by Peter Mark Roget for his Roget's Thesaurus.

While some works called "thesauri", such as Roget's Thesaurus, group words in a hierarchical hypernymic taxonomy of concepts, others are organised alphabetically[4][2] or in some other way.

Most thesauri do not include definitions, but many dictionaries include listings of synonyms.

Some thesauri and dictionary synonym notes characterise the distinctions between similar words, with notes on their "connotations and varying shades of meaning".[5] Some synonym dictionaries are primarily concerned with differentiating synonyms by meaning and usage. Usage manuals such as Fowler's Dictionary of Modern English Usage or Garner's Modern English Usage often prescribe appropriate usage of synonyms.

Writers sometimes use thesauri to avoid repetition of words – elegant variation – which is often criticised by usage manuals: "Writers sometimes use them not just to vary their vocabularies but to dress them up too much".[6]



The word "thesaurus" comes from Latin thēsaurus, which in turn comes from Greek θησαυρός (thēsauros) 'treasure, treasury, storehouse'.[7] The word thēsauros is of uncertain etymology.[7][8][9]

Until the 19th century, a thesaurus was any dictionary or encyclopedia,[9] as in the Thesaurus Linguae Latinae (Dictionary of the Latin Language, 1532), and the Thesaurus Linguae Graecae (Dictionary of the Greek Language, 1572). It was Roget who introduced the meaning "collection of words arranged according to sense", in 1852.[7]


Peter Mark Roget, author of Roget's thesaurus

In antiquity, Philo of Byblos authored the first text that could now be called a thesaurus. In Sanskrit, the Amarakosha is a thesaurus in verse form, written in the 4th century.

The study of synonyms became an important theme in 18th-century philosophy, and Condillac wrote, but never published, a dictionary of synonyms.[10][11]

Some early synonym dictionaries include:

  • John Wilkins, An Essay Towards a Real Character, and a Philosophical Language and Alphabetical Dictionary (1668) is a "regular enumeration and description of all those things and notions to which names are to be assigned". They are not explicitly synonym dictionaries — in fact, they do not even use the word "synonym" — but they do group synonyms together.[12][13][14]
  • Gabriel Girard, La Justesse de la langue françoise, ou les différentes significations des mots qui passent pour synonymes (1718)[15]
  • John Trusler, The Difference between Words esteemed Synonyms, in the English Language; and the proper choice of them determined (1766)[16]
  • Hester Lynch Piozzi, British Synonymy (1794)[17]
  • James Leslie, Dictionary of the Synonymous Words and Technical Terms in the English Language (1806)[18]
  • George Crabb, English Synonyms Explained (1818)[19]

Roget's Thesaurus, first compiled in 1805 by Peter Mark Roget, and published in 1852, follows John Wilkins' semantic arrangement of 1668. Unlike earlier synonym dictionaries, it does not include definitions or aim to help the user choose among synonyms. It has been continuously in print since 1852 and remains widely used across the English-speaking world.[20] Roget described his thesaurus in the foreword to the first edition:[21]

It is now nearly fifty years since I first projected a system of verbal classification similar to that on which the present work is founded. Conceiving that such a compilation might help to supply my deficiencies, I had, in the year 1805, completed a classed catalogue of words on a small scale, but on the same principle, and nearly in the same form, as the Thesaurus now published.





Roget's original thesaurus was organized into 1000 conceptual Heads (e.g., 806 Debt) organized into a four-level taxonomy. For example, debt is classed under V.ii.iv:[22]

Class five, Volition: the exercise of the will
Division Two: Social volition
Section 4: Possessive Relations
Subsection 4: Monetary relations.

Each head includes direct synonyms: Debt, obligation, liability, ...; related concepts: interest, usance, usury; related persons: debtor, debitor, ... defaulter (808); verbs: to be in debt, to owe, ... see Borrow (788); phrases: to run up a bill or score, ...; and adjectives: in debt, indebted, owing, .... Numbers in parentheses are cross-references to other Heads.

The book starts with a Tabular Synopsis of Categories laying out the hierarchy,[23] then the main body of the thesaurus listed by the Head, and then an alphabetical index listing the different Heads under which a word may be found: Liable, subject to, 177; debt, 806; duty, 926.[24]

Some recent versions have kept the same organization, though often with more detail under each Head.[25] Others have made modest changes such as eliminating the four-level taxonomy and adding new heads: one has 1075 Heads in fifteen Classes.[26]

Some non-English thesauri have also adopted this model.[27]

In addition to its taxonomic organization, the Historical Thesaurus of English (2009) includes the date when each word came to have a given meaning. It has the novel and unique goal of "charting the semantic development of the huge and varied vocabulary of English".

Different senses of a word are listed separately. For example, three different senses of "debt" are listed in three different places in the taxonomy:[28]
A sum of money that is owed or due; a liability or obligation to pay

Trade and Finance
Management of Money
Indebtedness [noun]

An immaterial debt; is an obligation to do something

Duty or obligation

An offence requiring expiation (figurative, Biblical)

Aspects of faith
instance of



Other thesauri and synonym dictionaries are organized alphabetically.

Most repeat the list of synonyms under each word.[29][30][31][32]

Some designate a principal entry for each concept and cross-reference it.[33][34][35]

A third system interfiles words and conceptual headings. Francis March's Thesaurus Dictionary gives for liability: CONTINGENCY, CREDIT–DEBT, DUTY–DERELICTION, LIBERTY–SUBJECTION, MONEY, each of which is a conceptual heading.[36] The CREDIT—DEBT article has multiple subheadings, including Nouns of Agent, Verbs, Verbal Expressions, etc. Under each are listed synonyms with brief definitions, e.g. "Credit. Transference of property on promise of future payment." The conceptual headings are not organized into a taxonomy.

Benjamin Lafaye's Synonymes français (1841) is organized around morphologically related families of synonyms (e.g. logis, logement),[37] and his Dictionnaire des synonymes de la langue française (1858) is mostly alphabetical, but also includes a section on morphologically related synonyms, which is organized by prefix, suffix, or construction.[11]

Contrasting senses


Before Roget, most thesauri and dictionary synonym notes included discussions of the differences among near-synonyms, as do some modern ones.[32][31][30][5]

Merriam-Webster's Dictionary of Synonyms is a stand-alone modern English synonym dictionary that does discuss differences.[33] In addition, many general English dictionaries include synonym notes.

Several modern synonym dictionaries in French are primarily devoted to discussing the precise demarcations among synonyms.[38][11]

Additional elements


Some include short definitions.[36]

Some give illustrative phrases.[32]

Some include lists of objects within the category (hyponyms), e.g. breeds of dogs.[32]



Bilingual synonym dictionaries are designed for language learners. One such dictionary gives various French words listed alphabetically, with an English translation and an example of use.[39] Another one is organized taxonomically with examples, translations, and some usage notes.[40]

Information science and natural language processing


In library and information science, a thesaurus is a kind of controlled vocabulary.

A thesaurus can form part of an ontology and be represented in the Simple Knowledge Organization System (SKOS).[41]

Thesauri are used in natural language processing for word-sense disambiguation[42] and text simplification for machine translation systems.[43]

See also



  • W.E. Collinson, "Comparative Synonymics: Some Principles and Illustrations", Transactions of the Philological Society 38:1:54–77, November 1939, doi:10.1111/j.1467-968X.1939.tb00202.x
  • Gerda Hassler, "Lafaye's Dictionnaire des synonymes in the History of Semantics" in Sheli Embleton, John E. Joseph, Hans-Josef Hiederehe, The Emergence of the Modern Language Sciences, John Benjamins 1999, ISBN 1556197594, p. 1:27–40
  • Werner Hüllen, "Roget's Thesaurus, deconstructed" in Historical Dictionaries and Historical Dictionary Research, papers from the International Conference on Historical Lexicography and Lexicology, University of Leicester, 2002, Max Niemeyer Verlag 2004, ISBN 3484391235, p. 83–94
  • Werner Hüllen, A history of Roget's thesaurus : origins, development, and design, Oxford University Press 2004, ISBN 0199254729
  • Werner Hüllen, Networks and Knowledge in Roget's Thesaurus, Oxford, January 2009, doi:10.1093/acprof:oso/9780199553235.001.0001, ISBN 0199553238
  • Gertrude E. Noyes, "The Beginnings of the Study of Synonyms in England", Publications of the Modern Language Association of America (PMLA) 66:6:951–970 (December 1951) doi:10.2307/460151 JSTOR 460151
  • Eric Stanley, "Polysemy and Synonymy and how these Concepts were Understood from the Eighteenth Century onwards in Treatises, and Applied in Dictionaries of English" in Historical Dictionaries and Historical Dictionary Research, papers from the International Conference on Historical Lexicography and Lexicology, University of Leicester, 2002, Max Niemeyer Verlag 2004, ISBN 3484391235, p. 157–184


  1. ^ "thesaurus, n.", OED Online, Oxford University Press, retrieved 2023-01-21
  2. ^ a b Oxford thesaurus of English. Maurice Waite (3rd ed.). Oxford: Oxford University Press. 2009. ISBN 978-0-19-956081-3. OCLC 321014234.{{cite book}}: CS1 maint: others (link)
  3. ^ Roget, Peter. 1852. Thesaurus of English Language Words and Phrases.
  4. ^ The Merriam-Webster thesaurus. Springfield, Massachusetts: Merriam-Webster. 2005. ISBN 978-0-87779-637-4. OCLC 57506786.
  5. ^ a b American Heritage Dictionary of the English Language, 5th edition, Houghton Mifflin Harcourt 2011, ISBN 9780547041018, p. xxvii
  6. ^ Edwin L. Battistella, "Beware the thesaurus", OUPblog, "Oxford University Press's Academic Insights for the Thinking World", February 11, 2018
  7. ^ a b c "thesaurus". Online Etymology Dictionary.
  8. ^ R. S. P. Beekes, Etymological Dictionary of Greek, Brill, 2009, p. 548.
  9. ^ a b Oxford English Dictionary s.v.
  10. ^ Embleton
  11. ^ a b c B. Lafaye, Dictionnaire des synonymes de la langue française, Hachette 1869, 3rd edition
  12. ^ John Wilkins, An Essay Towards a Real Character, and a Philosophical Language, London 1668 full text
  13. ^ John Wilkins, William Lloyd (anonymously), An Alphabetical Dictionary Wherein all English Words According to their Various Significations, Are either referred to their Places in the Philosophical Tables, Or explained by such Words as are in those Tables, London 1668 full text
  14. ^ Natascia Leonardi, "An Analysis of a Seventeenth Century Conceptual Dictionary with an Alphabetical List of Entries and a Network Definition Structure: John Wilkins' and William Lloyd's An Alphabetical Dictionary (1668)" in Historical Dictionaries and Historical Dictionary Research, papers from the International Conference on Historical Lexicography and Lexicology, University of Leicester, 2002, Max Niemeyer Verlag 2004, ISBN 3484391235, p. 39-52
  15. ^ Gabriel Girard, La Justesse de la langue françoise, ou les différentes significations des mots qui passent pour synonymes, Paris 1718, full text
  16. ^ John Trusler (anonymously), The Difference between Words esteemed Synonyms, in the English Language; and the proper choice of them determined, London, 1766 full text
  17. ^ Hester Lynch Piozzi, British Synonymy; or, an Attempt Regulating the Choice of Words in Familiar Conversation, Dublin 1794 full text
  18. ^ James Leslie, Dictionary of the Synonymous Words and Technical Terms in the English Language, Edinburgh, 1806 full text
  19. ^ George Crabb, English Synonyms Explained, in Alphabetical Order with Copious Illustrations and Examples Drawn from the Best Writers, 2nd edition, London 1818 full text
  20. ^ Hüllen, Werner (2003). "Introduction - Oxford Scholarship". oxfordscholarship.com. doi:10.1093/acprof:oso/9780199254729.001.0001. ISBN 978-0-19-925472-9. Retrieved 26 March 2018.
  21. ^ Roget, P. M. (1982). "Prefact to the first edition, 1852". In Lloyd, Susan M. (ed.). Roget's Thesaurus of English Words and Phrases (New ed.). Harlow: Longman. p. xix.
  22. ^ Peter Mark Roget, Thesaurus of English words and phrases, classified so as to facilitate the expression of ideas, 1853, V.ii.iv, p. 204
  23. ^ Roget, op.cit. p. xxvi
  24. ^ Roget, op.cit. p. 349
  25. ^ e.g., George Davidson, ed., Thesaurus of English words and phrases (150th Anniversary Edition), Penguin, 2002, ISBN 0141004428, p. 454
  26. ^ Barbara Ann Kipfer, ed., Roget's International Thesaurus, 7th edition, Collins Reference, 2010, ISBN 9780061715228
  27. ^ Daniel Péchoin, Thésaurus Larousse, Larousse 1991, ISBN 9782033201074
  28. ^ Christian Kay, Jane Roberts, Michael Samuels, Irené Wotherspoon, Historical Thesaurus of the Oxford English Dictionary, Oxford University Press 2009, ISBN 9780199208999, p. ix
  29. ^ Longman Synonym Dictionary, Rodale Press and Longman Group, 1986, ISBN 0582893224
  30. ^ a b Charlton Laird, Michael Agnes, eds., Webster's New World Roget's A-Z Thesaurus, Macmillan USA, 3rd edition, 1971, ISBN 0028632818
  31. ^ a b Christine A. Lindberg, The Oxford American Thesaurus of Current English, Oxford University Press, 1999, ISBN 0195133757
  32. ^ a b c d Oxford Thesaurus of English, 3rd edition, 2009, ISBN 9780199560813
  33. ^ a b Merriam-Webster's Dictionary of Synonyms : Choose Words with Precision, 1994, ISBN 0877799067 uses an asterisk
  34. ^ Henri Bertaud du Chazaud, Dictionnaire de synonyms et contraires, Le Robert "Les Usuels", 1998, ISBN 2850364568
  35. ^ Roger Boussinot, Dictionnaire des synonymes, analogies et antonymes, Bordas 1981, ISBN 2040120092
  36. ^ a b Francis Andrew March, Francis A. March, Jr., March's Thesaurus and Dictionary of the English Language (issued under the editorial supervision of Norman Cousins), Doubleday, 1968, p. 598 full text, 1906 edition
  37. ^ Pierre Benjamin Lafaye, Synonymes français, Paris 1841 full text
  38. ^ Henri Bénac, Dictionnaire des synonymes, Hachette 1956, ISBN 2010112199 (1982 edition)
  39. ^ R.E. Batchelor, M.H. Offord, Using French Synonyms, Cambridge University Press, 1993, ISBN 0521372771
  40. ^ Marie-Noëlle Lamy, The Cambridge French-English Thesaurus, Cambridge University Press, 1998, ISBN 0521563488
  41. ^ Miles, Alistair; Bechhofer, Sean (2009). "SKOS simple knowledge organization system reference". W3C Recommendation. 18: W3C.
  42. ^ Yarowsky, David. "Word-sense disambiguation using statistical models of Roget's categories trained on large corpora." Proceedings of the 14th conference on Computational linguistics-Volume 2. Association for Computational Linguistics, 1992.
  43. ^ Siddharthan, Advaith. "An architecture for a text simplification system." Language Engineering Conference, 2002. Proceedings. IEEE, 2002.