'Complacent' once meant 'pleasing' — from Latin 'placere.' It soured into smug self-satisfaction.
Showing smug or uncritical satisfaction with oneself or one's achievements, especially when unaware of impending dangers.
From Latin 'complacentem,' present participle of 'complacēre' (to be very pleasing, to please greatly), a compound of 'com-' (intensive prefix, with, together) + 'placēre' (to please, to be agreeable). The PIE root is *pleh₂k- (to be flat, smooth, pleasing) — related to *pleh₂- (flat), source of Latin 'plānus' (flat, level) and Greek 'platys' (broad). In early English use (1650s–1750s) 'complacent' meant simply 'pleasing' or 'self-satisfied in a positive sense
The words 'complacent' and 'complaisant' come from the same Latin verb but diverged in English: 'complacent' (smug self-satisfaction) is negative, while 'complaisant' (eagerly obliging) is neutral or positive. French kept only 'complaisant,' making the English distinction a uniquely English semantic split.
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