blockbuster vs megahit

blockbuster and megahit both are nouns.

Word	Noun	Adjective	Verb	Adverb
blockbuster	Yes	No	No	No
megahit	Yes	No	No	No

As nouns, blockbuster and megahit are synonyms defined as:

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

Other synonyms of blockbuster include smash hit.

blockbuster (noun)	megahit (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)