rest (v.2)youdaoicibaDictYouDict[rest 词源字典]
"to be left, remain," mid-15c., from Old French rester "to remain," from Latin restare "stand back, be left," from re- "back" (see re-) + stare "to stand," from PIE root *sta- "to stand, set down, make or be firm" (see stet). Partially confused and merged with the other verb rest. Sense of "to continue to be" is in rest assured. Transitive sense of "to keep, cause to continue to remain" was common in 16c.-17c., "used with a predicate adjective following and qualifying the object" [Century Dictionary], hence phrase rest you merry (1540s); God rest you merry, gentlemen, often is mis-punctuated.[rest etymology, rest origin, 英语词源]