cotter pin vs cotter

cotter pin and cotter both are nouns.

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

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

cotter pin: a cotter consisting of a split pin that is secured (after passing through a hole) by splitting the ends apart
cotter: fastener consisting of a wedge or pin inserted through a slot to hold two other pieces together

Other hypernyms of cotter pin include cottar.

cotter pin (noun)	cotter (noun)
a cotter consisting of a split pin that is secured (after passing through a hole) by splitting the ends apart	fastener consisting of a wedge or pin inserted through a slot to hold two other pieces together
	a medieval English villein
	a peasant farmer in the Scottish Highlands