decayyoudaoicibaDictYouDict[decay 词源字典]
decay: [15] The notion underlying decay and its close relative decadence is of a ‘falling off’ from a condition of health or perfection. Decay comes from Old Northern French decair, a descendant of Vulgar Latin *dēcadere, which in turn came from Latin dēcidere, a compound verb formed from the prefix dē- ‘down, off, away’ and cadere ‘fall’ (source of English case and a wide range of related words). Decadence [16] was acquired via the medieval derivative dēcadentia. To the same word-family belongs deciduous [17], from Latin dēciduus, literally denoting the ‘falling off’ of leaves from trees.
=> accident, case, chance, decadence, deciduous[decay etymology, decay origin, 英语词源]
decay (v.)youdaoicibaDictYouDict
late 15c., "to decrease," from Anglo-French decair, Old North French decair (Old French decheoir, 12c., Modern French déchoir) "to fall, set (of the sun), weaken, decline, decay," from Vulgar Latin *decadere "to fall off," from de- (see de-) + Latin cadere "to fall" (see case (n.1)). Meaning "decline, deteriorate" is c. 1500; that of "to decompose, rot" is from 1570s. Related: Decayed; decaying.
decay (n.)youdaoicibaDictYouDict
mid-15c., "deterioration, decline in value," from decay (v.). Meaning "gradual decrease in radioactivity" is from 1897.