The Collaborative International Dictionary of English v.0.48:

Squeal \Squeal\, n.
   A shrill, sharp, somewhat prolonged cry.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Squeal \Squeal\ (skw[=e]l), v. i. [imp. & p. p. Squealed
   (skw[=e]ld); p. pr. & vb. n. Squealing.] [Of Scand. origin;
   cf. Sw. sqv[aum]la, Norw. skvella. Cf. Squeak, Squall.]
   1. To cry with a sharp, shrill, prolonged sound, as certain
      animals do, indicating want, displeasure, or pain.
      [1913 Webster]

   2. To turn informer; to betray a secret. [Slang]
      [1913 Webster]

WordNet (r) 3.0 (2006):

squeal
    n 1: a high-pitched howl
    v 1: utter a high-pitched cry, characteristic of pigs [syn:
         squeal, oink]
    2: confess to a punishable or reprehensible deed, usually under
       pressure [syn: confess, squeal, fink]

Moby Thesaurus II by Grady Ward, 1.0:

194 Moby Thesaurus words for "squeal":
   babble, bark, battle cry, bawl, bay, be indiscreet, be unguarded,
   bear witness against, beep, bell, bellow, betray,
   betray a confidence, birdies, bitch, blab, blabber, blare, blast,
   blat, blate, bleat, blooping, blow, blow the horn,
   blow the whistle, blubber, blurping, blurt, blurt out, boom, bray,
   breathe, bugle, buzz, cackle, call, caterwaul, chant, cheer, chirp,
   clarion, complain, coo, creak, crow, cry, distortion, drawl,
   exclaim, fanfare, feedback, fink, flourish of trumpets, flute,
   flutter, fluttering, gasp, give away, give tongue, give voice,
   grate, gripe, growl, grunt, hail, halloo, hiss, hissing, holler,
   hollo, honk, hoot, howl, howling, hum, hurrah, inform,
   inform against, inform on, keen, leak, let drop, let fall,
   let slip, lilt, low, meow, mew, mewl, miaow, moo, motorboating,
   mumble, murmur, mutter, narc, nark, neigh, nicker, pant, peach,
   peal, pimp, pipe, pule, raise a howl, rallying cry, rasp, rat,
   reveal a secret, roar, rumble, scratching, screak, scream, screech,
   sell out, shall, shout, shredding, shriek, shrill, sibilate, sigh,
   sing, skirl, skreigh, snap, snarl, snitch, snitch on, snort, sob,
   sound, sound a tattoo, sound taps, spill, spill the beans, squall,
   squawk, squeak, squeals, static, stool, talk, tantara, tantarara,
   taps, tarantara, tattle, tattle on, tattoo, tell on, tell secrets,
   tell tales, testify against, thunder, toot, tootle, troat, trumpet,
   trumpet blast, trumpet call, turn informer, twang, tweedle,
   ululate, ululation, wail, war cry, war whoop, warble, whicker,
   whine, whinny, whisper, whistle, whistles, whoop, wind, woomping,
   wow, wowwows, wrawl, yammer, yap, yawl, yawp, yell, yelp, yip,
   yo-ho, yowl