truck vs tow truck

truck and tow truck both are nouns.

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

As nouns, tow truck is a hyponym of truck; that is, tow truck is a word with a more specific, narrower meaning than truck:

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

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

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