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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).
Latin, literally "not master of one's mind."
non compos mentis non com·pos men·tis (nŏn kŏm'pəs měn'tĭs)
Not of sound mind and hence not legally responsible; mentally incompetent.
Latin for “There's no disputing about taste.” Another version of this saying is “There's no accounting for taste.”
A phrase used to describe someone who is out of his or her mind and therefore not legally responsible for his or her actions: “It was determined by the court that the killer was non compos mentis.” From Latin, meaning “not having control of the mind.”
A person who is no longer favored or welcome: “After my angry words with the manager, I am persona non grata at the video store.” From Latin, meaning “an unacceptable person.”