truck vs tanker truck

truck and tanker truck both are nouns.

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

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

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

truck (noun)	tanker truck (noun)
an automotive vehicle suitable for hauling	a motor vehicle designed to carry liquefied loads, dry bulk cargo or gases on roads.
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)	tanker truck (verb)
convey (goods etc.) by truck