WordNet (r) 3.0 (2006):

yip
    n 1: a sharp high-pitched cry (especially by a dog) [syn: yip,
         yelp, yelping]
    v 1: bark in a high-pitched tone; "the puppies yelped" [syn:
         yelp, yip, yap]

Moby Thesaurus II by Grady Ward, 1.0:

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