booster unit vs takeoff rocket

booster unit and takeoff rocket both are nouns.

Word	Noun	Adjective	Verb	Adverb
booster unit	Yes	No	No	No
takeoff rocket	Yes	No	No	No

As nouns, booster unit and takeoff rocket are synonyms defined as:

Other synonyms of booster unit include booster, booster rocket, takeoff booster.

booster unit (noun)	takeoff rocket (noun)
the first stage of a multistage rocket	the first stage of a multistage rocket