sizz vs let out

sizz and let out both are verbs.

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

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

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

sizz (verb)	let out (verb)
make a sharp hissing sound, as if to show disapproval	make (clothes) larger
express or utter with a hiss	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