Iodhadh is the Irish name of the twentieth letter of the Ogham alphabet, ᚔ. In Old Irish, the letter name was idad. Its phonetic value is [i]. The original meaning of the letter name is uncertain, but it is likely an artificially altered pair with edad, much like Gothic pairþra, qairþra, and may refer to "yew".
|Ogham letters ᚛ᚑᚌᚐᚋᚁᚂᚃᚓᚇᚐᚅ᚜|
|ᚄ||[s]||Sail||ᚎ||[st], [ts], [sw]||Straif|
(rare, sounds uncertain)
|ᚕ||[ea], [k], [x], [eo]||Éabhadh|
The medieval glossators all assign "yew" as the meaning of the letter name referred to by the kennings, though Idad is not a word attested in its own right. Idad as "yew" is glossed by these later commentators as deriving from a modified form of ibar originally. However, this is unlikely to be the Old Irish word that gave the letter its value of "yew", as the cognate Welsh efwr and Gallo-Roman eburos point to a Primitive Irish *eburas, and ibar was used (with qualifiers) to refer to a whole range of evergreen shrubs.
It is more likely that the Old Irish word that gave the letter its ascribed meaning was éo, from the Primitive Irish *iwas (c.f. Welsh ywen, Gaulish ivo-, Proto-Indo-European *iwo- "yew"). McManus suggests that the original letter names for edad and idad were likely *eburas (or *esox) and *iwas, hence their values [e] and [i] respectively, with confusion arising in the medieval period as the language evolved.
In the medieval kennings, called Bríatharogaim or Word Ogham the verses associated with idad are:
sinem fedo - "oldest tree" in the Bríatharogam Morann mic Moín
caínem sen - "fairest of the ancients" in the Bríatharogam Mac ind Óc
- Schrijver, Peter (2015). "The meaning of Celtic *eburos". In Oudaer, Guillaume; Hily, Gaël; Le Bihan, Hervé (eds.). Mélanges en l'honneur de Pierre-Yves Lambert. Rennes: TIR. pp. 65–76.
- McManus, Damian (1988). "Irish Letter-Names and Their Kennings". Ériu. 39: 127–168. JSTOR 30024135.
- Auraicept na n-Éces Calder, George, Edinburgh, John Grant (1917), reprint Four Courts Press (1995), ISBN 1-85182-181-3
- McManus, Damian. (1991). A guide to Ogam. Maynooth: An Sagart. ISBN 1-870684-17-6. OCLC 24181838.