retrorocket

American  

[re-troh-rok-it] / ˈrɛ troʊˌrɒk ɪt /

Or retro-rocket

noun

1. a small, auxiliary rocket engine, forming a part of a larger rocket vehicle and having its exhaust nozzle pointed toward the direction of flight, for decelerating the larger rocket, separating one stage from another, etc.

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retrorocket British  

/ ˈrɛtrəʊˌrɒkɪt /

noun

1. Often shortened to: retro.  a small auxiliary rocket engine on a larger rocket, missile, or spacecraft, that produces thrust in the opposite direction to the direction of flight in order to decelerate the vehicle or make it move backwards

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Etymology

Origin of retrorocket

First recorded in 1945–50; retro- + rocket ¹