booster unit vs takeoff booster

booster unit and takeoff booster both are nouns.

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

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

booster unit and takeoff booster: the first stage of a multistage rocket

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

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