sing vs let out

sing and let out both are verbs.

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

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

sing: divulge confidential information or secrets
let out: make known to the public information that was previously known only to a few people or that was meant to be kept a secret

Other hypernyms of sing include break, bring out, disclose, discover, divulge, expose, give away, let on, reveal, uncover, unwrap.

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

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

sing (verb)	let out (verb)
make a whining, ringing, or whistling sound	make (clothes) larger
divulge confidential information or secrets	make known to the public information that was previously known only to a few people or that was meant to be kept a secret
to make melodious sounds	express audibly; utter sounds (not necessarily words)
produce tones with the voice	bring out of a specific state
deliver by singing