grunt vs let loose

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

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

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

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

grunt (noun)	let loose (noun)
medium-sized tropical marine food fishes that utter grunting sounds when caught
the short low gruff noise of the kind made by hogs
an unskilled or low-ranking soldier or other worker

grunt (verb)	let loose (verb)
issue a grunting, low, animal-like noise	express audibly; utter sounds (not necessarily words)
	turn loose or free from restraint