hold in vs restrain

hold in and restrain both are verbs.

Word	Noun	Adjective	Verb	Adverb
hold in	No	No	Yes	No
restrain	No	No	Yes	No

As verbs, restrain is a hypernym of hold in; that is, restrain is a word with a broader meaning than hold in:

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

Other hypernyms of hold in include hold back, keep, keep back.

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