hold back vs refrain

hold back is not a noun while refrain is a noun.

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

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

Other hypernyms of hold back include forbear.

hold back (noun)	refrain (noun)
	the part of a song where a soloist is joined by a group of singers

hold back (verb)	refrain (verb)
prevent the action or expression of	choose not to consume
hold back, as of a danger or an enemy; check the expansion or influence of	resist doing something
hold back; keep from being perceived by others
secure and keep for possible future use or application
wait before acting
refrain from doing