sustainer vs booster

sustainer and booster both are nouns.

Word	Noun	Adjective	Verb	Adverb
sustainer	Yes	No	No	No
booster	Yes	No	No	No

As nouns, booster is a hypernym of sustainer; that is, booster is a word with a broader meaning than sustainer:

Other hypernyms of sustainer include admirer, champion, friend, protagonist, supporter.

sustainer (noun)	booster (noun)
someone who upholds or maintains	an additional dose that makes sure the first dose was effective
	the first stage of a multistage rocket
	an amplifier for restoring the strength of a transmitted signal
	a thief who steals goods that are in a store
	someone who is an active supporter and advocate
	a person who backs a politician or a team etc.