The Collaborative International Dictionary of English v.0.48:

Croak \Croak\, v. t.
   To utter in a low, hoarse voice; to announce by croaking; to
   forebode; as, to croak disaster.
   [1913 Webster]

         The raven himself is hoarse,
         That croaks the fatal entrance of Duncan. --Shak.
   [1913 Webster]

         Two ravens now began to croak
         Their nuptial song.                      --Wordsworth.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Croak \Croak\, n.
   The coarse, harsh sound uttered by a frog or a raven, or a
   like sound.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Croak \Croak\ (kr[=o]k), v. i. [imp. & p. p. Croaked.
   (kr[=o]kt); p. pr. & vb. n. Croaking.] [From the primitive
   of AS. cracettan to croak as a raven; akin to G. kr[aum]chzen
   to croak, and to E. creak, crake.]
   1. To make a low, hoarse noise in the throat, as a frog, a
      raven, or a crow; hence, to make any hoarse, dismal sound.
      [1913 Webster]

            Loud thunder to its bottom shook the bog,
            And the hoarse nation croaked.        --Pope.
      [1913 Webster]

   2. To complain; especially, to grumble; to forebode evil; to
      utter complaints or forebodings habitually.
      [1913 Webster]

            Marat . . . croaks with reasonableness. --Carlyle.
      [1913 Webster]

WordNet (r) 3.0 (2006):

croak
    n 1: a harsh hoarse utterance (as of a frog) [syn: croak,
         croaking]
    v 1: pass from physical life and lose all bodily attributes and
         functions necessary to sustain life; "She died from
         cancer"; "The children perished in the fire"; "The patient
         went peacefully"; "The old guy kicked the bucket at the age
         of 102" [syn: die, decease, perish, go, exit,
         pass away, expire, pass, kick the bucket, cash in
         one's chips, buy the farm, conk, give-up the ghost,
         drop dead, pop off, choke, croak, snuff it] [ant:
         be born]
    2: utter a hoarse sound, like a raven [syn: croak, cronk]
    3: make complaining remarks or noises under one's breath; "she
       grumbles when she feels overworked" [syn: murmur, mutter,
       grumble, croak, gnarl]