Disappointment (3)
'disappointment' is the definition.
(something or someone which lets you down)
This is the entire clue.
'disappointment' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for let-down that I've seen before include "Anticlimax" , "It's disappointing" , "Disappointment" .)
'disappointment' is the definition.
(a damp squib is something underwhelming)
This is the entire clue.
(Other definitions for damp squib that I've seen before include "Something that fails to have the expected impact" , "set up by a guy?" , "Firework that doesn't" , "Let-down" , "Something less impressive than expected" .)
(Other definitions for dud that I've seen before include "Explosive not detonating" , "A palindromic failure" , "Thing that fails to work" , "Not functioning" , "Failing in its function" .)