smasher vs smash hit

smasher and smash hit both are nouns.

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

As nouns, smash hit is a hyponym of smasher; that is, smash hit is a word with a more specific, narrower meaning than smasher:

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

Other hyponyms of smasher include blockbuster, megahit, sleeper.

smasher (noun)	smash hit (noun)
a conspicuous success	an unusually successful hit with widespread popularity and huge sales (especially a movie or play or recording or novel)
a very attractive or seductive looking woman
a person who smashes something