A multigraph (or pleongraph) is a sequence of letters that behaves as a unit and is not the sum of its parts, such as English ⟨ch⟩ or French ⟨eau⟩. The term is infrequently used, as the number of letters is usually specified:
- Digraph (two letters, as ⟨ch⟩ or ⟨ea⟩)
- Trigraph (three letters, as ⟨tch⟩ or ⟨eau⟩)
- Tetragraph (four letters, as German ⟨tsch⟩)
- Pentagraph (five letters)
- Hexagraph (six letters)
- Heptagraph (seven letters)
Combinations longer than tetragraphs are unusual. The German pentagraph ⟨tzsch⟩ has largely been replaced by ⟨tsch⟩, remaining only in proper names such as ⟨Poenitzsch⟩ or ⟨Fritzsche⟩. Except for doubled trigraphs like German ⟨schsch⟩, hexagraphs are found only in Irish vowels, where the outside letters indicate whether the neighboring consonant is "broad" or "slender". However, these sequences are not predictable. The hexagraph ⟨oidhea⟩, for example, where the ⟨o⟩ and ⟨a⟩ mark the consonants as broad, represents the same sound (approximately the vowel in English write) as the trigraph ⟨adh⟩, and with the same effect on neighboring consonants.
The seven-letter German sequence ⟨schtsch⟩, used to transliterate Russian ⟨щ⟩, as in ⟨Borschtsch⟩ for ⟨борщ⟩ "borscht", is a sequence of a trigraph ⟨sch⟩ and a tetragraph ⟨tsch⟩ rather than a heptagraph. Likewise, the Juu languages have been claimed to have a heptagraph ⟨dts’kx’⟩, but this is also a sequence, of ⟨dts’⟩ and ⟨kx’⟩.
Beyond the Latin alphabet, Morse code uses hexagraphs for several punctuation marks, and the dollar sign ⟨$⟩ is a heptagraph, ⟨· · · — · · —⟩. Longer sequences are considered ligatures, and are transcribed as such in the Latin alphabet.