A backhanded stroke, hit, or blow; also slang for a bribe or dishonest payment made secretly.
From 'backhand' + '-er' (agent suffix). The slang sense emerged in British English in the 20th century, possibly from the idea of slipping something sideways or underhandedly.
In British slang, a 'backhander' is a bribe, which is darkly clever—you're literally using a word for an indirect stroke to describe an indirect, underhanded deal that avoids facing ethics directly.
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