reef vs let down

reef is a noun but let down is not a noun.

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

As verbs, let down is a hypernym of reef; that is, let down is a word with a broader meaning than reef:

Other hypernyms of reef include bring down, get down, lower, take down.

reef (noun)	let down (noun)
one of several strips across a sail that can be taken in or rolled up to lessen the area of the sail that is exposed to the wind
a submerged ridge of rock or coral near the surface of the water

reef (verb)	let down (verb)
roll up (a portion of a sail) in order to reduce its area	fail to meet the hopes or expectations of
reduce (a sail) by taking in a reef	move something or somebody to a lower position
lower and bring partially inboard