A clever trick or deceptive move, or something done quickly and cunningly.
From 'swift' meaning quick or rapid, with '-y' suffix added informally to create a noun. Primarily British slang that evolved in the 20th century. The word plays on the idea of something fast and tricky happening so quickly you might miss it.
A 'swifty' is the perfect word for a con that works because it happens so fast—it's deception at the speed of a bird in flight! British soldiers and schoolboys popularized this slang to describe clever tricks that caught you off-guard. The word captures how the best tricks rely on speed and misdirection happening simultaneously.
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