scream vs let loose

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

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

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

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

scream (noun)	let loose (noun)
sharp piercing cry
a joke that seems extremely funny
a high-pitched noise resembling a human cry

scream (verb)	let loose (verb)
utter a sudden loud cry	express audibly; utter sounds (not necessarily words)
utter or declare in a very loud voice	turn loose or free from restraint
make a loud, piercing sound