sing vs let loose

sing and let loose both are verbs.

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

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

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

sing (verb)	let loose (verb)
make a whining, ringing, or whistling sound	express audibly; utter sounds (not necessarily words)
divulge confidential information or secrets	turn loose or free from restraint
to make melodious sounds
produce tones with the voice
deliver by singing