The tail fin of a fish, or an action where a vehicle's rear slides side-to-side like a fish's tail movement.
From Old English 'fisc' + 'tail' from Old Norse 'tagl.' The metaphorical use for vehicle movement emerged in 20th-century driving terminology.
The fishtailing phenomenon in cars happens for the exact same physics reason fish tails propel them forward—a sideways motion creates forward momentum through fluid resistance.
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