introduced 1947 (at 14th conference of the Union Internationale de Chimie) as a prefix for units of one thousand-millionth part (now "one-billionth"), from Greek nanos "a dwarf." According to Watkins, this is originally "little old man," from nannos "uncle," masc. of nanna "aunt" (see nana), but Beekes calls it "An onomatopoeic word of unknown origin." Earlier nano- was used as a prefix to mean "dwarf, dwarfish," and still it is used in a non-scientific sense of "very small."
before vowels nephr-, word-forming element meaning "kidney, kidneys," from Greek nephros "a kidney" (plural nephroi), from PIE *negwhro- "kidney" (source also of Latin nefrones, Old Norse nyra, Dutch nier, German Niere "kidney").
before vowels nitr-, word-forming element used scientifically and indicating nitrogen, nitrate, or nitric acid; from Greek nitron (see nitre).
a prefix used freely in English and meaning "not, lack of," or "sham," giving a negative sense to any word, 14c., from Anglo-French noun-, from Old French non-, from Latin non "not, by no means, not at all, not a," from Old Latin noenum "not one" (*ne oinom, from PIE root *ne- "not" + PIE root *oi-no- "one, unique"). In some cases perhaps from Middle English non "not" (adj.), from Old English nan (see not). "It differs from un- in that it denotes mere negation or absence of the thing or quality, while un- often denotes the opposite of the thing or quality" [Century Dictionary].