quiet (adj.)
late 14c., "peaceable, at rest, restful, tranquil," from Old French quiet and directly from Latin quietus "calm, at rest, free from exertion," from quies (genitive quietis) "rest" (see quiet (n.)). As an adverb from 1570s. Related: Quietly; quietness.
quiet (n.)
c.1300, "freedom from disturbance or conflict; calm, stillness," from Old French quiete "rest, repose, tranquility" and directly from Latin quies (genitive quietis) "a lying still, rest, repose, peace," from PIE root *kweie- (2) "to rest, be quiet" (cognates: Old Persian shiyati-, Avestan shaiti- "well-being;" Avestan shyata- "happy;" Gothic hveila, Old English hwil "space of time;" see while (n.)). Late 14c. as "inactivity, rest, repose."
quiet (v.)
late 14c., "subdue, lessen," from quiet (adj.) and in part from Latin quietare. From mid-15c. as "to make silent, cause to be quiet;" intransitive sense of "become quiet, be silent" is from 1791. Related: Quieted; quieting.