groan vs let out

groan is a noun but let out is not a noun.

Word	Noun	Adjective	Verb	Adverb
groan	Yes	No	Yes	No
let out	No	No	Yes	No

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

Other hypernyms of groan include emit, let loose, utter.

groan (noun)	let out (noun)
an utterance expressing pain or disapproval

groan (verb)	let out (verb)
indicate pain, discomfort, or displeasure	make (clothes) larger
	make known to the public information that was previously known only to a few people or that was meant to be kept a secret
	express audibly; utter sounds (not necessarily words)
	bring out of a specific state