A river in Gondor, the fifth in the region of Lebennin (LotR/750), and so translated “Fifth” (VT42/14). It is simply lefnui “fifth” uses as a name and was thus pronounced [levnui], but Tolkien preferred the spelling Lefnui because “v” rarely appears before consonants in English (VT42/14).
Conceptual Development: When first mentioned in maps for the Lord of the Rings drafts from the 1940s, this name was first given as N. Lhefned >> Lhefneg (WR/437, TI/312), apparently earlier Noldorin words for “fifth”.
lemenya archaic ordinal adj. "fifth", replaced by lempëa (VT42:25)