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]
"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.