fixing vs fastening

fixing and fastening both are nouns.

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

As nouns, fixing and fastening are synonyms defined as:

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

Other synonyms of fixing include fastener, holdfast.

fixing (noun)	fastening (noun)
the act of putting something in working order again	the act of fastening things together
the sterilization of an animal	restraint that attaches to something or holds something in place
(histology) the preservation and hardening of a tissue sample to retain as nearly as possible the same relations they had in the living body
restraint that attaches to something or holds something in place