fastening vs fastener

fastening and fastener both are nouns.

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

As nouns, fastening and fastener are synonyms defined as:

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

Other synonyms of fastening include fixing, holdfast.

fastening (noun)	fastener (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	a person who fastens or makes fast