bellwether (n.)youdaoicibaDictYouDict[bellwether 词源字典]
mid-14c. (late 13c. in Anglo-Latin; late 12c. as a surname), from bell (n.) + wether; the lead sheep (on whose neck a bell was hung) of a domesticated flock. Figurative sense of "chief, leader" is from mid-14c.[bellwether etymology, bellwether origin, 英语词源]