fire truck vs motortruck

fire truck and motortruck both are nouns.

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

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

fire truck: any of various large trucks that carry firemen and equipment to the site of a fire
motortruck: an automotive vehicle suitable for hauling

Other hypernyms of fire truck include truck.

fire truck (noun)	motortruck (noun)
any of various large trucks that carry firemen and equipment to the site of a fire	an automotive vehicle suitable for hauling