restraint vs holdfast

restraint and holdfast both are nouns.

Word	Noun	Adjective	Verb	Adverb
restraint	Yes	No	No	No
holdfast	Yes	No	No	No

As nouns, holdfast is a hyponym of restraint; that is, holdfast is a word with a more specific, narrower meaning than restraint:

restraint (noun)	holdfast (noun)
the act of controlling by restraining someone or something	restraint that attaches to something or holds something in place
a device that retards something's motion
discipline in personal and social activities
lack of ornamentation
a rule or condition that limits freedom
the state of being physically constrained