Source : Webster's Revised Unabridged Dictionary (1913)

Whew \Whew\ (hw[=u]), n. & interj.
   A sound like a half-formed whistle, expressing astonishment,
   scorn, or dislike.

   {Whew duck}, the European widgeon. [Prov. Eng.]

Whew \Whew\, v. i.
   To whistle with a shrill pipe, like a plover. [Prov. Eng. &
   Scot.]