tow truck vs truck

tow truck and truck both are nouns.

Word	Noun	Adjective	Verb	Adverb
tow truck	Yes	No	No	No
truck	Yes	No	Yes	No

As nouns, truck is a hypernym of tow truck; that is, truck is a word with a broader meaning than tow truck:

tow truck: a truck equipped to hoist and pull wrecked cars (or to remove cars from no-parking zones)
truck: an automotive vehicle suitable for hauling

Other hypernyms of tow truck include motortruck.

tow truck (noun)	truck (noun)
a truck equipped to hoist and pull wrecked cars (or to remove cars from no-parking zones)	an automotive vehicle suitable for hauling
	a handcart that has a frame with two low wheels and a ledge at the bottom and handles at the top; used to move crates or other heavy objects

tow truck (verb)	truck (verb)
	convey (goods etc.) by truck