Booster rocket and Rocket engine

Booster rocket noun - The first stage of a multistage rocket.

Rocket engine and booster rocket are semantically related. In some cases you can use "Rocket engine" instead a noun phrase "Booster rocket".

Rocket engine noun - A jet engine containing its own propellant and driven by reaction propulsion.

Booster rocket and rocket engine are semantically related. Sometimes you can replace phrase "Booster rocket" with "Rocket engine", this phrases are similar.