croak vs let loose

croak is a noun but let loose is not a noun.

Word	Noun	Adjective	Verb	Adverb
croak	Yes	No	Yes	No
let loose	No	No	Yes	No

As verbs, let loose is a hypernym of croak; that is, let loose is a word with a broader meaning than croak:

Other hypernyms of croak include emit, let out, utter.

croak (noun)	let loose (noun)
a harsh hoarse utterance (as of a frog)

croak (verb)	let loose (verb)
pass from physical life and lose all bodily attributes and functions necessary to sustain life	express audibly; utter sounds (not necessarily words)
make complaining remarks or noises under one's breath	turn loose or free from restraint
utter a hoarse sound, like a raven