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compliment [compliment 词源字典]: compliment: [17] Compliment and complement, so often confused, are in effect doublets. They come from the same ultimate source, Latin complēmentum, a noun derived from complēre ‘fill up, finish’ (source of English complete and accomplish). English borrowed complement direct from Latin in the 14th century in the sense ‘fulfilment, accomplishment’, and by the 16th century this had developed the more specific metaphorical meaning ‘fulfilment of the obligation of politeness’ – hence ‘polite words of praise’.

But then in the 17th century came competition in the form of compliment, also meaning ‘polite words of praise’. This also came from Latin complēmentum, but along a circuitous route via Vulgar Latin *complimentum, Spanish cumplimiento, and French compliment. It gradually took over from complement in this ‘flattering’ sense, while complement went on to develop its leading current meaning, ‘counterpart’, in the 19th century.
=> accomplish, complement, complete, comply, expletive, plenary, plenty[compliment etymology, compliment origin, 英语词源]
compliment (n.): "An act, or expression of civility, usually understood to include some hypocrisy, and to mean less than it declares" [Johnson], 1570s, complement, via French compliment (17c.), from Italian complimento "expression of respect and civility," from Vulgar Latin *complire, for Latin complere "to complete" (see complete (adj.)), via notion of "complete the obligations of politeness." Same word as complement but by a different etymological route; differentiated by spelling after 1650.
graciousness (n.): late 14c., "attractiveness, agreeable quality," early 15c., from gracious + -ness. From 1630s as "courtesy, politeness."
impolite (adj.): 1610s, "unrefined, rough," from Latin impolitus "unpolished, rough, unrefined," from assimilated form of in- "not, opposite of" (see in- (1)) + politus "polished" (see polite). Sense of "discourteous, ill-mannered" is from 1739. Related: Impolitely; impoliteness.
polite (adj.): late 14c., "polished, burnished" (mid-13c. as a surname), from Latin politus "refined, elegant, accomplished," literally "polished," past participle of polire "to polish, to make smooth" (see polish (v.)). Used literally at first in English; sense of "elegant, cultured" is first recorded c. 1500, that of "behaving courteously" is 1748 (implied in politely). Related: Politeness.