keep vs hold back

keep is a noun but hold back is not a noun.

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

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

Other synonyms of keep include keep back, restrain.

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

keep (noun)	hold back (noun)
the main tower within the walls of a medieval castle or fortress
a cell in a jail or prison
the financial means whereby one lives

keep (verb)	hold back (verb)
prevent (food) from rotting	prevent the action or expression of
prevent the action or expression of	hold back, as of a danger or an enemy; check the expansion or influence of
stick to correctly or closely	hold back; keep from being perceived by others
maintain by writing regular records	secure and keep for possible future use or application
supply with necessities and support	wait before acting
hold and prevent from leaving	refrain from doing
retain possession of
look after; be the keeper of; have charge of
retain rights to
maintain for use and service
have as a supply
store or keep customarily
stop (someone or something) from doing something or being in a certain state
allow to remain in a place or position or maintain a property or feature
conform one's action or practice to
behave as expected during of holidays or rites
cause to continue in a certain state, position, or activity
supply with room and board
maintain in safety from injury, harm, or danger
fail to spoil or rot
continue a certain state, condition, or activity
to rear