Croak (krk), v. i. [imp. & p. p. Croaked. (krp. pr. & vb. n. Croaking.]
Etymology: [From the primitive of AS. cracettan to croak as a raven; akin to G. kr 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. Loud thunder to its bottom shook the bog, And the hoarse nation croaked. Pope.
2. To complain; especially, to grumble; to forebode evil; to utter complaints or forebodings habitually. Marat . . . croaks with reasonableness. Carlyle.
2 other Webster entries under this spelling
Croak, v. t.
To utter in a low, hoarse voice; to announce by croaking; to forebode; as, to croak disaster. The raven himself is hoarse, That croaks the fatal entrance of Duncan. Shak. Two ravens now began to croak Their nuptial song. Wordsworth.
Croak, n.
The coarse, harsh sound uttered by a frog or a raven, or a like sound.
Shades of meaning
Fernald has no entry of its own for croak; he lists it under complain.
He lists it without comment; the entries above explain its neighbors.