Where [j] (“y”) or [w] became final after short final vowels vanished, these final [j], [w] first became [i], [u], then the resulting [i] and [u] became [e] and [o] in most cases. The clearest examples of this development are ᴹ✶winyā > gwini > Ilk. gwine (Ety/WIN) and ᴹ✶wilwā > gwelu > Ilk. gwelo (Ety/WIL). This changed did not occur where the final vowel was part of a diphthong: gwau (Ety/WĀ).

There are a several examples where this change did not occur in the case of [-u]: Dor. ganu, Dor. gelu and Dor. hedhu. All of these examples were marked Doriathrin in The Etymologies, so perhaps this development did not occur in that dialect of Ilkorin, though it does seem to have occurred with Dor. (n)golo “magic, lore” (Ety/ÑGOL).