restrain vs restrainer

restrain is not a noun while restrainer is a noun.

Word	Noun	Adjective	Verb	Adverb
restrain	No	No	Yes	No
restrainer	Yes	No	No	No

restrain (noun)	restrainer (noun)
	a person who directs and restrains
	a chemical that is added to a photographic developer in order to retard development and reduce the amount of fog on a film

restrain (verb)	restrainer (verb)
prevent the action or expression of
to close within bounds, or otherwise limit or deprive of free movement
restrict (someone or something) so as to make free movement difficult
prevent (someone or something) from doing something