Green’s Dictionary of Slang

a disappointment.

1866		London Misc. 3 Mar. 57: Bug-hunting (robbing drunken men) was about the best game out, and he added, ‘I don’t think that’s no little let-down for a cove as has been tip-topper in his time.’ [F&H].
1917		G. De S. Wentworth-James Man Market 226: Well, well, in small as in large things it was all the same – a ‘let-down’ every time!
1932		(con. 1917–19) Dos Passos Nineteen Nineteen in USA (1966) 414: It was a let down to get back to the dying elms of the Yard.
1947		J. Maclaren-Ross Of Love And Hunger 103: The schoolroom was a let-down. It wasn’t got up like the rest of the building.
1951		M. Spillane One Lonely Night 50: Too much of a letdown, I guessed.
1965		C. Brown Manchild in the Promised Land (1969) 188: When she told me no, it was a big letdown.
1971		D. Goines Dopefiend (1991) 210: You might get a hell of a letdown.
1981		J. Ellroy Brown’s Requiem 129: I’ve been waiting for this moment for over ten years, but it feels like a big letdown.
1999		K. Sampson Powder 268: Given she hadn’t seen him for nearly a fortnight their reunion had been a let-down.
2000		Indep. on Sun. Rev. 16 Jan. 28: Do the words ‘Millenium Dome’ pop into your ‘mind’ at this point, along with the words ‘complete let-down’.