A helicopter, or alternatively, a tool or device used for chopping, such as a kitchen utensil or motorcycle with modified handlebars.
From 'chop' plus agent suffix '-er.' The helicopter sense emerged in the 1950s from the chopping motion of rotor blades. The motorcycle meaning developed in the 1960s American custom bike culture, referring to 'chopped' (modified) motorcycles.
It's remarkable how 'chopper' demonstrates the playful creativity of slang - the same word describes kitchen tools, helicopters, and custom motorcycles, all united by some form of cutting or chopping motion. The helicopter usage became so dominant that many people don't realize it started as casual military slang.
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