sing vs sing along

sing and sing along both are verbs.

Word	Noun	Adjective	Verb	Adverb
sing	No	No	Yes	No
sing along	No	No	Yes	No

As verbs, sing along is a hyponym of sing; that is, sing along is a word with a more specific, narrower meaning than sing:

sing (verb)	sing along (verb)
make a whining, ringing, or whistling sound	sing with a choir or an orchestra
divulge confidential information or secrets
to make melodious sounds
produce tones with the voice
deliver by singing