The Collaborative International Dictionary of English v.0.48:

Yowl \Yowl\, v. i. [See Yawl, v. i.]
   To utter a loud, long, and mournful cry, as a dog; to howl;
   to yell.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Yowl \Yowl\, n.
   A loud, protracted, and mournful cry, as that of a dog; a
   howl.
   [1913 Webster]

WordNet (r) 3.0 (2006):

yowl
    n 1: a very loud utterance (like the sound of an animal); "his
         bellow filled the hallway" [syn: bellow, bellowing,
         holla, holler, hollering, hollo, holloa, roar,
         roaring, yowl]
    v 1: cry loudly, as of animals; "The coyotes were howling in the
         desert" [syn: howl, wrawl, yammer, yowl]
    2: utter shrieks, as of cats [syn: yowl, caterwaul]

Moby Thesaurus II by Grady Ward, 1.0:

79 Moby Thesaurus words for "yowl":
   bark, battle cry, bawl, bay, bell, bellow, blare, blat, blate,
   bleat, bray, call, caterwaul, cheer, cry, cry out, dolorous tirade,
   give tongue, give voice, groan, hail, halloo, holler, hollo, hoot,
   howl, hurrah, jeremiad, keen, lament, low, make an outcry, meow,
   mew, mewl, miaow, moan, moo, murmur, mutter, neigh, nicker, outcry,
   plaint, planctus, pule, rallying cry, roar, screak, scream,
   screech, shout, shriek, sob, squall, squawk, squeak, squeal,
   tirade, troat, ululate, ululation, wail, wail of woe, war cry,
   war whoop, whicker, whimper, whine, whinny, whoop, yammer, yap,
   yawl, yawp, yell, yelp, yip, yo-ho