chopper · noun1
chopper · noun, verb2
From the onomatopoeia for the "chop-chop" sound emitted by the main rotor blades of the Bell 47 'OH-13 Sioux' "Angel of Mercy" helicopter, encountered by troops during the Korean War.
Chopper · noun3
From chopper (“helicopter”), because of the distinctive beating noise of the engine.
Etymology from Wiktionary, CC BY-SA 4.0.