fire engine vs motortruck

fire engine and motortruck both are nouns.

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

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

fire engine: 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 engine include truck.

fire engine (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