smash hit vs blockbuster

smash hit and blockbuster both are nouns.

Word	Noun	Adjective	Verb	Adverb
smash hit	Yes	No	No	No
blockbuster	Yes	No	No	No

As nouns, smash hit and blockbuster are synonyms defined as:

smash hit and blockbuster: an unusually successful hit with widespread popularity and huge sales (especially a movie or play or recording or novel)

Other synonyms of smash hit include megahit.

smash hit (noun)	blockbuster (noun)
an unusually successful hit with widespread popularity and huge sales (especially a movie or play or recording or novel)	an unusually successful hit with widespread popularity and huge sales (especially a movie or play or recording or novel)
	a large bomb used to demolish extensive areas (as a city block)