id n.

Old English geon "that (over there)," from Proto-Germanic *jaino- (source also of Old Frisian jen, Old Norse enn, Old High German ener, Middle Dutch ghens, German jener, Gothic jains "that, you"), from PIE pronominal stem *i- (source also of Sanskrit ena-, third person pronoun, anena "that;" Latin idem "the same," id "it, that one;" Old Church Slavonic onu "he;" Lithuanian ans "he"). As an adverb from late 15c., a shortening of yonder.

late 14c., originally an adverb, "moreover, in addition," from Latin item (adv.) "likewise, just so, moreover," probably from ita "thus," id "it" (see id) + adverbial ending -tem (compare idem "the same").

The Latin adverb was used to introduce a new fact or statement, and in French and English it was used before every article in an enumeration (such as an inventory or bill). This practice led to the noun sense "an article of any kind" (1570s). Meaning "detail of information" (especially in a newspaper) is from 1819; item "sexually linked unmarried couple" is 1970, probably from notion of being an item in the gossip columns.