tank truck vs truck

tank truck and truck both are nouns.

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

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

tank truck: a motor vehicle designed to carry liquefied loads, dry bulk cargo or gases on roads.
truck: an automotive vehicle suitable for hauling

Other hypernyms of tank truck include motortruck.

tank truck (noun)	truck (noun)
a motor vehicle designed to carry liquefied loads, dry bulk cargo or gases on roads.	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

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