DuckCorp Dico

Found one definition

1.                 From The Collaborative International Dictionary of English v.0.48:
                   
   
   
                   
                     
   Moo \Moo\ (m[=oo]), v. i. [imp. & p. p. Mooed; p. pr. & vb. n.
      Mooing.] [Of imitative origin.]
      To make the noise of a cow; to low; -- a child's word.
      [1913 Webster]