interj.
Pronunciation: ' w ō , ' h ō , ' hw ō
Function: verb imperative
Etymology: Middle English whoo, who
Date: 15th century
1 ― a command (as to a draft animal) to stand still
2 : cease or slow a course of action or a line of thought : pause to consider or reconsider ― often used to express a strong reaction (as alarm or astonishment)