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
Often shortened to: retro
retrorocket in American English
(ˈrɛtroʊˌrɑkɪt), ˈretˌro-rocket (ˈrɛtroʊˌrɑkɪt)
US
noun
a small rocket on a larger rocket or spacecraft, that produces thrust in a directionopposite to the direction of flight in order to reduce speed, as for maneuvering