truck vs pickup truck

truck and pickup truck both are nouns.

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

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

truck (noun)	pickup truck (noun)
an automotive vehicle suitable for hauling	a light truck with an open body and low sides and a tailboard
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)	pickup truck (verb)
convey (goods etc.) by truck