Etymology
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calm (n.)

c. 1400, "absence of storm or wind," from the adjective or from Old French calme, carme "stillness, quiet, tranquility," or directly from Old Italian (see calm (adj.)). Figurative sense "peaceful manner, mild bearing" is from early 15c.; that of "freedom from agitation or passion" is from 1540s.

Aftir the calm, the trouble sone Mot folowe. ["Romance of the Rose," c. 1400]
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calm (v.)
late 14c., "to become calm," from Old French calmer or from calm (adj.). Also transitive, "to make still or quiet" (1550s). Related: Calmed; calming.
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calm (adj.)
late 14c., of the sea, "windless, without motion or agitation;" of a wind, "light, gentle," perhaps via Old French calme "tranquility, quiet," or directly from Old Italian calma "quiet, fair weather," which probably is from Late Latin cauma "heat of the mid-day sun" (in Italy, a time when everything rests and is still), from Greek kauma "heat" (especially of the sun), from kaiein "to burn" (see caustic). Spelling influenced by Latin calere "to be hot." Figurative application to social or mental conditions, "free from agitation or passion," is from 1560s.
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calmly (adv.)
"quietly, peacefully," 1590s, from calm (adj.) + -ly (2).
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calmness (n.)
"quietness, stillness, tranquility," 1510s, from calm (adj.) + -ness.
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becalm (v.)
1550s in nautical use, "deprive a ship of wind," from be- + calm. Meaning "make calm or still" is from 1610s. Related: Becalmed; becalming.
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calmative (adj.)
"quieting excessive action," by 1831, from French calmatif; see calm (adj.) + -ative. A Greek-Latin hybrid; purists prefer sedative, but OED writes that "The Latinic suffix is here defensible on the ground of It. and Sp. calmar, F. calmer ...." Also as a noun, "a quieting drug" (1847).
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Honolulu 
chief city of Hawaii, from Hawaiian hono "port" + lulu "calm."
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placid (adj.)

"gentle, quiet, undisturbed, serene, calm," 1620s, from French placide (15c.) and directly from Latin placidus "pleasing, peaceful, quiet, gentle, still, calm," from placere "to please" (see please). Related: Placidly; placidness.

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serenade (n.)
1640s, "musical performance at night in open air" (especially one given by a lover under the window of his lady), from French sérénade (16c.), from Italian serenata "an evening song," literally "calm sky," from sereno "the open air," noun use of sereno "clear, calm," from Latin serenus "peaceful, calm, serene." Sense influenced by Italian sera "evening," from Latin sera, fem. of serus "late." Meaning "piece of music suitable for a serenade" is attested from 1728.
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