decline vs disdain

decline and disdain both are nouns.

Word	Noun	Adjective	Verb	Adverb
decline	Yes	No	Yes	No
disdain	Yes	No	Yes	No

As verbs, disdain is a hyponym of decline; that is, disdain is a word with a more specific, narrower meaning than decline:

Other hyponyms of decline include freeze off, pooh-pooh, reject, scorn, spurn, turn down, contract out, regret, repudiate, disobey.

decline (noun)	disdain (noun)
a downward slope or bend	a communication that indicates lack of respect by patronizing the recipient
a gradual decrease; as of stored charge or current	lack of respect accompanied by a feeling of intense dislike
change toward something smaller or lower
a condition inferior to an earlier condition; a gradual falling off from a better state; decline

decline (verb)	disdain (verb)
grow smaller	reject with contempt
grow worse	look down on with disdain
show unwillingness towards
inflect for number, gender, case, etc.
go down
fall in value
not accept as true