Dud Middle English dudde, a cloak
A bomb, shell, mine or explosive round that fails to explode.
That which is ineffectual. Any object that fails to do what it should.
The bridge is still standing because that last bomb was a dud.
That party was a dud, I didn't have any fun at all.
Sources
The American Heritage Dictionary of the English Language, Fourth Edition
http://www.dictionary.com/
http://www.m-w.com/
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