Irish: Iodhadh is the Irish name of the twentieth letter of the Ogham alphabet, ᚔ. In Old Irish, the letter name was Irish, Old (to 900);: idad. Its phonetic value is [i]. The original meaning of the letter name is uncertain, but it is likely an artificially altered pair with Irish: [[eadhadh (letter)|edad]], much like Gothic Gothic: [[peordh|pairþra, qairþra]], and may refer to "yew".
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.[1]
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.[2]
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
lúth lobair (?) - "energy of an infirm person (?)" in the Bríatharogam Con Culainn.[3] [4]