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prefix meaning "not, lack of," or "sham," 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 *ne "not" + *oi-no-; see one). In some cases perhaps from Middle English non "not" (adj.), from Old English nan (see not).