thruster vs rocket engine

thruster and rocket engine both are nouns.

Word	Noun	Adjective	Verb	Adverb
thruster	Yes	No	No	No
rocket engine	Yes	No	No	No

As nouns, rocket engine is a hypernym of thruster; that is, rocket engine is a word with a broader meaning than thruster:

thruster: a small rocket engine that provides the thrust needed to maneuver a spacecraft
rocket engine: a jet engine containing its own propellant and driven by reaction propulsion

Other hypernyms of thruster include rocket.

thruster (noun)	rocket engine (noun)
a small rocket engine that provides the thrust needed to maneuver a spacecraft	a jet engine containing its own propellant and driven by reaction propulsion
one who intrudes or pushes himself forward