relevancy vs cogency

relevancy and cogency both are nouns.

Word	Noun	Adjective	Verb	Adverb
relevancy	Yes	No	No	No
cogency	Yes	No	No	No

As nouns, cogency is a hyponym of relevancy; that is, cogency is a word with a more specific, narrower meaning than relevancy:

Other hyponyms of relevancy include materiality, point, applicability, pertinence, pertinency.

relevancy (noun)	cogency (noun)
the relation of something to the matter at hand	the quality of being valid and rigorous
	persuasive relevance