Source : Webster's Revised Unabridged Dictionary (1913)

Mouse \Mouse\, v. i. [imp. & p. p. {Moused}; p. pr. & vb. n.
   {Mousing}.]
   1. To watch for and catch mice.

   2. To watch for or pursue anything in a sly manner; to pry
      about, on the lookout for something.