cotter vs fastener

cotter and fastener both are nouns.

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

As nouns, fastener is a hypernym of cotter; that is, fastener is a word with a broader meaning than cotter:

cotter: fastener consisting of a wedge or pin inserted through a slot to hold two other pieces together
fastener: restraint that attaches to something or holds something in place

Other hypernyms of cotter include fastening, fixing, holdfast.

cotter (noun)	fastener (noun)
fastener consisting of a wedge or pin inserted through a slot to hold two other pieces together	restraint that attaches to something or holds something in place
a medieval English villein	a person who fastens or makes fast
a peasant farmer in the Scottish Highlands