restrain vs curb

restrain is not a noun while curb is a noun.

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

As verbs, curb is a hyponym of restrain; that is, curb is a word with a more specific, narrower meaning than restrain:

restrain: prevent the action or expression of
curb: lessen the intensity of; temper; hold in restraint; hold or keep within limits

As verbs, curb is a hyponym of restrain; that is, curb is a word with a more specific, narrower meaning than restrain:

restrain: restrict (someone or something) so as to make free movement difficult
curb: keep to the curb

Other hyponyms of restrain include bridle, clog.

restrain (noun)	curb (noun)
	the act of restraining power or action or limiting excess
	an edge between a sidewalk and a roadway consisting of a line of curbstones (usually forming part of a gutter)
	a horse's bit with an attached chain or strap to check the horse

restrain (verb)	curb (verb)
prevent the action or expression of	place restrictions on
to close within bounds, or otherwise limit or deprive of free movement	keep to the curb
restrict (someone or something) so as to make free movement difficult	lessen the intensity of; temper; hold in restraint; hold or keep within limits
prevent (someone or something) from doing something