cetiddeirgni

cét- (“first”) +‎ id- (“it”) (relative) +‎ do·rigni (“who has done”)

• IPA^(key): [kʲedʲiˈdʲerʲɣʲnʲi]

The affixed pronoun id- is pronounced [iðʲ] and triggers lenition, so the expected pronunciation would be *[kʲedʲiðʲˈðʲerʲɣʲnʲi]; however, a geminate [ðʲðʲ] regularly delenites to [dʲ].

cetid·deirgni

1. (he/she/who) who has done it first
   • c. 800–825, Diarmait, Milan Glosses on the Psalms, published in Thesaurus Palaeohibernicus (reprinted 1987, Dublin Institute for Advanced Studies), edited and with translations by Whitley Stokes and John Strachan, vol. I, pp. 7–483, Ml. 124^b3

     Ní du ṡémigud pectha at·ber-som inso .i. combad dó fa·cherred: “ní sní cetid·deirgni ⁊ ní sní dud·rigni nammá”; acht is do chuingid dílguda dosom, amal du·rolged dïa aithrib íar n-immarmus.

     It is not to palliate sin that he says this, i.e. so that he might put it for this: “we have not done it first and we have not done it only”; but it is to seek forgiveness for himself, as his fathers had been forgiven after sinning.

     (literally, “…“it is not we who have done it first…”)