This word is not translated. It could be related to Quenya íre "when". Some scholars also consider that it could be the form taken by the article i before a vowel, on a pattern similar to ah . To this respect, it might be interesting to note the ir was the allative/dative form of the article in the old Gnomish lexicon, PE/11:9
conjunction. (?) when
is simply a variant of the definite article.
adverb. when, (lit.) during what
@@@ based on the theory that ned = “during”
Word Gloss ned “first, one more; first; during” man “*what, who”
?ir (not used in questions but to indicate time, as in ”when I saw you, I was glad”). This is one of several possible interpretations of the word, which occurs in a Sindarin poem untranslated by Tolkien (ir Isil ammen Eruchín…síla, ?”when the Moon shines for us Children of Eru…”, The Lays of Beleriand p. 354). By another interpretation, ir is simply a variant of the definite article.(relative pronoun), see THAT
(not used in questions but to indicate time, as in ”when