nightcap (n.)youdaoicibaDictYouDict[nightcap 词源字典]
also night-cap, late 14c., "covering for the head, worn in bed," from night + cap (n.). In the alcoholic sense, it is attested from 1818. American English sense of "final event in a sporting contest" (especially the second game of a baseball double-header) is from 1939.[nightcap etymology, nightcap origin, 英语词源]