fail vs let down

fail and let down both are verbs.

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

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

Other hypernyms of fail include disappoint.

fail (verb)	let down (verb)
stop operating or functioning	fail to meet the hopes or expectations of
deteriorate	move something or somebody to a lower position
prove insufficient
disappoint, prove undependable to; abandon, forsake
become bankrupt or insolvent; fail financially and close
be unsuccessful
fail to get a passing grade
fail to do something; leave something undone
judge unacceptable
be unable
fall short in what is expected