hold on vs hold back

hold on and hold back both are verbs.

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

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

hold on (verb)	hold back (verb)
be persistent, refuse to stop	prevent the action or expression of
stop and wait, as if awaiting further instructions or developments	hold back, as of a danger or an enemy; check the expansion or influence of
hold the phone line open	hold back; keep from being perceived by others
hold firmly	secure and keep for possible future use or application
retain possession of	wait before acting
	refrain from doing