Elvish name for Ireland in the earliest Lost Tales (LT2/283), appearing also as Íwerin or Iverindor in the Gnomish Lexicon (GL/18). In a Discord post from 2025-03-14, Valerie suggested Tolkien based this on Proto-Celtic *Īweriū / Iveriu > Ériu > (modern) Éire “Ireland”, which seems very plausible to me. She further suggested it may be related to G. ivrin “fertile” which could be have a similar inspiration from (possibly) related Primitive Indo-European *pi-wer- “fertile”.