Disappoint (4)
'disappoint' is the definition.
(I know that fail is a more specific form of the action disappoint)
This is all the clue.
(Other definitions for fail that I've seen before include "Stop working properly" , "Fall short" , "Break down" , "Don't succeed" , "Go wrong" .)
'disappoint' is the definition.
(synonyms)
This is all the clue.
(Other definitions for let down that I've seen before include "Disappoint, fail to support" , "Leave in the lurch" , "blow" , "Lower" , "Failed - to deflate a tyre - disappointed" .)