"become quiet or calm, become silent," 1821, from Latin quiescere "to rest," from suffixed form of PIE root *kweie- "to rest, be quiet."
a form of mysticism which consists in abnegation of all exercise of the will and purely passive meditation on God and divine things, 1680s, from Italian quietismo, literally "passiveness," from quieto "calm, at rest," from Latin quietus "free; calm, resting" (from PIE root *kweie- "to rest, be quiet").
Originally in reference to the mysticism of Miguel Molinos (1640-1697), Spanish priest in Rome, whose "Guida spirituale" was published 1675 and condemned by the Inquisition in 1685. Related: Quietist; Quietistic.
The name is from Latin halcyon, alcyon, from Greek halkyon, variant (perhaps a misspelling) of alkyon "kingfisher," a word of unknown origin. The explanation that this is from hals "sea; salt" (see halo-) + kyon "conceiving," present participle of kyein "to conceive," literally "to swell" (see cumulus) probably is ancient folk-etymology to explain a loan-word from a non-Indo-European language. Identified in mythology with Halcyone, daughter of Aeolus, who when widowed threw herself into the sea and became a kingfisher.
mid-15c., of a day, "clear, fair, calm," from Old French serein and directly from Latin serenus "peaceful, calm, clear, unclouded" (of weather); figuratively "cheerful, glad, tranquil"(from PIE root *ksero- "dry," source also of Greek xeros "dry, arid;" see xerasia).
In English, the word has been applied to persons, characters, etc. since 1630s: "tranquil, unruffled." Related: Serenely. Middle English also had serenous (mid-15c.), of places, "having clear, fair weather."
"conciliatory, intended to placate or appease," 1630s, from Latin placatorius "pertaining to appeasing," from placat-, past-participle stem of placare "to calm, appease, quiet, soothe, assuage," causative of placere "to please" (see please).
"rest, repose, quiet, tranquility," 1590s, from French quiétude (c. 1500) or directly from Late Latin quietudo, from Latin quietus "free; calm, resting" (from PIE root *kweie- "to rest, be quiet"). In the same sense quietness is attested from mid-15c.
"act of pleasing, pacifying, or conciliating," 1580s, from French placation (16c.), from Latin placationem (nominative placatio) "an appeasing, pacifying, quieting," noun of action from past-participle stem of placare "to calm, appease, quiet, soothe, assuage," causative of placere "to please" (see please).
Sense of "easy to understand, free from obscurity of meaning, marked by intellectual clarity" first recorded 1786. Lucid interval "period of calm or temporary sanity" (1580s) is from Medieval Latin lucida intervalla (plural), common in medieval legal documents (non est compos mentis, sed gaudet lucidis intervallis, etc.). The notion probably is of a period of calm and clear during a storm. Related: Lucidly; lucidness (1640s).