let down vs incline

let down is not a noun while incline is a noun.

Word	Noun	Adjective	Verb	Adverb
let down	No	No	Yes	No
incline	Yes	No	Yes	No

As verbs, incline is a hyponym of let down; that is, incline is a word with a more specific, narrower meaning than let down:

Other hyponyms of let down include reef, depress, dip.

let down (noun)	incline (noun)
	an inclined surface connecting two levels
	an elevated geological formation

let down (verb)	incline (verb)
fail to meet the hopes or expectations of	make receptive or willing towards an action or attitude or belief
move something or somebody to a lower position	feel favorably disposed or willing
	be at an angle
	lower or bend (the head or upper body), as in a nod or bow
	bend or turn (one's ear) towards a speaker in order to listen well
	have a tendency or disposition to do or be something; be inclined