Green’s Dictionary of Slang

croak n.

[croak v.2 (1)]

1. [mid-19C] supposed final speeches from the gallows and murderers’ confessions, usu. as peddled by street-sellers and possibly written by a hack journalist.

2. [mid–late 19C] a dying speech.

3. [late 19C–1940s] (also croaking) death.

4. [1910s] (US) a boring complainer, a whinger.

In phrases

do a croak (v.) (also pull the croak chain)

[late 19C–1920s] to die.

do a gun croak (v.)

[1900s–20s] (US) to shoot oneself dead.

on the croak

[late 19C] (US) on the verge of death, dying.