smash hit vs megahit

smash hit and megahit both are nouns.

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

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

smash hit and megahit: 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 blockbuster.

smash hit (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)