crestfallen (adj.)youdaoicibaDictYouDict[crestfallen 词源字典]
1580s, past participle adjective, but the verb crestfall is recorded only from 1610s, in reference to diseased horses, and is rare. It's possible that the image behind this use of the word is not cocks, as often is asserted, but horses.[crestfallen etymology, crestfallen origin, 英语词源]