masturbator vs frotteur

masturbator and frotteur both are nouns.

Word	Noun	Adjective	Verb	Adverb
masturbator	Yes	No	No	No
frotteur	Yes	No	No	No

As nouns, frotteur is a hyponym of masturbator; that is, frotteur is a word with a more specific, narrower meaning than masturbator:

masturbator: a person who practices masturbation
frotteur: someone who masturbates by rubbing against another person (as in a crowd)

Other hyponyms of masturbator include jerk-off, tosser, wanker.

masturbator (noun)	frotteur (noun)
a person who practices masturbation	someone who masturbates by rubbing against another person (as in a crowd)