collision vs smash-up

collision and smash-up both are nouns.

Word	Noun	Adjective	Verb	Adverb
collision	Yes	No	No	No
smash-up	Yes	No	No	No

As nouns, smash-up is a hyponym of collision; that is, smash-up is a word with a more specific, narrower meaning than collision:

Other hyponyms of collision include fender-bender, pileup, smash.

collision (noun)	smash-up (noun)
a conflict of opposed ideas or attitudes or goals	a serious collision (especially of motor vehicles)
an accident resulting from violent impact of a moving object
(physics) a brief event in which two or more bodies come together