droop (v.)youdaoicibaDictYouDict[droop 词源字典]
early 13c., from Old Norse drupa "to drop, sink, hang (the head)," from Proto-Germanic *drup-, from PIE *dhreu-, related to Old English dropian "to drop" (see drip). Related: Drooped; drooping. As a noun, from 1640s.[droop etymology, droop origin, 英语词源]