whoa (interj.)youdaoicibaDictYouDict[whoa 词源字典]
1620s, a cry to call attention from a distance, a variant of who. As a command to stop a horse, it is attested from 1843, a variant of ho. As an expression of delight or surprise (1980s) it has gradually superseded wow, which was very popular 1960s.[whoa etymology, whoa origin, 英语词源]