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]