tank truck vs motortruck

tank truck and motortruck both are nouns.

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

As nouns, motortruck is a hypernym of tank truck; that is, motortruck 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.
motortruck: an automotive vehicle suitable for hauling

Other hypernyms of tank truck include truck.

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