motortruck vs semi

motortruck and semi both are nouns.

Word	Noun	Adjective	Verb	Adverb
motortruck	Yes	No	No	No
semi	Yes	No	No	No

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

motortruck (noun)	semi (noun)
an automotive vehicle suitable for hauling	a trailer having wheels only in the rear; the front is supported by the towing vehicle
	a truck consisting of a tractor and trailer together
	one of the two competitions in the next to the last round of an elimination tournament