stand-by (n.)youdaoicibaDictYouDict[stand-by 词源字典]
also standby, 1796, "that which stands by one," originally nautical, of a vessel kept nearby for emergencies, from verbal phrase stand by "await, support, remain beside" (mid-13c.); see stand (v.) + by. Meaning "state of being ready for duty" is from 1946. In civil aviation, as an adjective meaning "without a booked ticket," from 1961. As an order to hold one's self in readiness, it is recorded from 1660s.[stand-by etymology, stand-by origin, 英语词源]