sing along vs sing

sing along and sing both are verbs.

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

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

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