Green’s Dictionary of Slang

croak v.2

[the death-rattle]

1. [early 19C+] (also croak it) to die; also in fig. use .

2. [early 19C+] to kill, to murder; thus croaking, n., a murder; croak artist, n., a murderer.

3. [20C+] as croak oneself, to commit suicide.

4. [1900s] (US campus) to fail an examination or a course [fig. use of sense 1].