The Collaborative International Dictionary of English v.0.48:

Moo \Moo\ (m[=o]), a., adv., & n.
   See Mo. [Obs.] --Chaucer.
   [1913 Webster]

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]

The Collaborative International Dictionary of English v.0.48:

Moo \Moo\, n.
   The lowing of a cow.
   [1913 Webster]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006):

MOO
       MUD Object Orientated (Internet, OOP, MUD)


Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "moo":
   bark, bawl, bay, bell, bellow, blare, blat, blate, bleat, bray,
   call, caterwaul, cry, give tongue, give voice, howl, low, meow,
   mew, mewl, miaow, neigh, nicker, pule, roar, screak, scream,
   screech, squall, squeak, squeal, troat, ululate, wail, whicker,
   whine, whinny, yap, yawl, yawp, yelp, yip, yowl