cottar vs cotter pin

cottar and cotter pin both are nouns.

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

As nouns, cotter pin is a hyponym of cottar; that is, cotter pin is a word with a more specific, narrower meaning than cottar:

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

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