The act of preventing someone's plan from succeeding or stopping a criminal attempt.
From Old French 'foiler' meaning to trample or crush, which entered English in the 13th century. The meaning shifted to 'defeat a plan' in the 1500s, possibly influenced by the idea of trampling someone's scheme underfoot.
The word 'foil' has a double life—it can mean both a thin metal sheet AND to thwart a plan. This split happened because both uses trace back to the idea of 'beating down,' though one evolved into the material sense (beaten metal sheets) and the other kept the abstract 'defeat' meaning.
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