hold back vs hold in

hold back and hold in both are verbs.

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

As verbs, hold in is a hyponym of hold back; that is, hold in is a word with a more specific, narrower meaning than hold back:

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

As verbs, hold back and hold in are synonyms defined as:

Other synonyms of hold back include conceal.

hold back (verb)	hold in (verb)
prevent the action or expression of	hold back; keep from being perceived by others
hold back, as of a danger or an enemy; check the expansion or influence of	lessen the intensity of; temper; hold in restraint; hold or keep within limits
hold back; keep from being perceived by others	close in
secure and keep for possible future use or application
wait before acting
refrain from doing