Rocket engine and Takeoff rocket

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

Takeoff rocket and rocket engine are semantically related. In some cases you can replace phrase "Takeoff rocket" with "Rocket engine", this phrases are similar.

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

Rocket engine and takeoff rocket are semantically related. You can use "Rocket engine" instead a noun phrase "Takeoff rocket".