turnover (n.)youdaoicibaDictYouDict[turnover 词源字典]
also turn-over, 1650s, "action of turning over," from the verbal phrase; see turn (v.) + over (adv.). As a kind of pastry tart, from 1798. Meaning "number of employees leaving a place and being replaced" is recorded from 1955.[turnover etymology, turnover origin, 英语词源]