\Pshaw\, interj. [Of imitative origin.]
Pish! pooch! -- an exclamation used as an expression of
contempt, disdain, dislike, etc. [Written also {psha}.]

\Pshaw\, v. i.
To express disgust or contemptuous disapprobation, as by the
exclamation `` Pshaw!''
      The goodman used regularly to frown and pshaw wherever
      this topic was touched upon.             --Sir W.
                                               Scott.