whoa
/hwəʊ/exclamation
1- used as a command to a horse to make it stop or slow down吁（用于吆喝马停下或放慢速度）。
1.1
- informal used as a greeting, to express surprise or interest, or to command attention〈非正式〉呀（用于打招呼, 表示惊讶、兴趣或引起注意等）：
whoa, that's huge!
呀, 真大！
词源
late Middle English: variant of HO2.