cotter vs holdfast

cotter and holdfast both are nouns.

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

As nouns, holdfast is a hypernym of cotter; that is, holdfast 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
holdfast: restraint that attaches to something or holds something in place

Other hypernyms of cotter include fastener, fastening, fixing.

cotter (noun)	holdfast (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 peasant farmer in the Scottish Highlands