holdfast vs fastener

holdfast and fastener both are nouns.

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

As nouns, holdfast and fastener are synonyms defined as:

holdfast and fastener: restraint that attaches to something or holds something in place

Other synonyms of holdfast include fastening, fixing.

holdfast (noun)	fastener (noun)
restraint that attaches to something or holds something in place	restraint that attaches to something or holds something in place
	a person who fastens or makes fast