drop dead vs croak

drop dead is not a noun while croak is a noun.

Word	Noun	Adjective	Verb	Adverb
drop dead	No	No	Yes	No
croak	Yes	No	Yes	No

As verbs, drop dead and croak are synonyms defined as:

drop dead and croak: pass from physical life and lose all bodily attributes and functions necessary to sustain life

drop dead (noun)	croak (noun)
	a harsh hoarse utterance (as of a frog)

drop dead (verb)	croak (verb)
pass from physical life and lose all bodily attributes and functions necessary to sustain life	pass from physical life and lose all bodily attributes and functions necessary to sustain life
	make complaining remarks or noises under one's breath
	utter a hoarse sound, like a raven