fastening vs holdfast

fastening and holdfast both are nouns.

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

As nouns, fastening and holdfast are synonyms defined as:

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

Other synonyms of fastening include fastener, fixing.

fastening (noun)	holdfast (noun)
the act of fastening things together	restraint that attaches to something or holds something in place
restraint that attaches to something or holds something in place