The Collaborative International Dictionary of English v.0.48:

Yelp \Yelp\, v. i. [imp. & p. p. Yelped; p. pr. & vb. n.
   Yelping.] [OE. yelpen, [yogh]elpen, to boast, boast
   noisily, AS. gielpan, gilpan, gylpan; akin to OHG. gelph
   arrogant: cf. Icel. gj[=a]lpa to yelp. Cf. Yap.]
   [1913 Webster]
   1. To boast. [Obs.]
      [1913 Webster]

            I keep [care] not of armes for to yelpe. --Chaucer.
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   2. To utter a sharp, quick cry, as a hound; to bark shrilly
      with eagerness, pain, or fear; to yaup.
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            A little herd of England's timorous deer,
            Mazed with a yelping kennel of French curs? --Shak.
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            At the least flourish of a broomstick or ladle, he
            would fly to the door with a yelping precipitation.
                                                  --W. Irving.
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The Collaborative International Dictionary of English v.0.48:

Yelp \Yelp\, n.
   A sharp, quick cry; a bark. --Chaucer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

yelp
    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:

118 Moby Thesaurus words for "yelp":
   air a grievance, bark, battle cry, bawl, bay, beef, bell, bellow,
   bellyache, bitch, blare, blat, blate, bleat, blubber, boom, bray,
   breathe, buzz, cackle, call, caterwaul, chant, cheer, chirp,
   clamor, complain, coo, crab, croak, crow, cry, drawl, exclaim,
   flute, fret, fret and fume, fuss, gasp, give tongue, give voice,
   gripe, groan, grouch, grouse, growl, grumble, grunt, hail, halloo,
   hiss, holler, hollo, hoot, howl, hurrah, keen, kick, lilt,
   lodge a complaint, low, meow, mew, mewl, miaow, moo, mumble,
   murmur, mutter, neigh, nicker, pant, pipe, pule, raise a howl,
   rallying cry, register a complaint, roar, rumble, screak, scream,
   screech, shout, shriek, sibilate, sigh, sing, snap, snarl, snort,
   sob, squall, squawk, squeak, squeal, take on, thunder, troat,
   trumpet, twang, ululate, wail, war cry, war whoop, warble, whicker,
   whine, whinny, whisper, whoop, yammer, yap, yawl, yawp, yell, yip,
   yo-ho, yowl