believer vs booster

believer and booster both are nouns.

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

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

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

believer (noun)	booster (noun)
a person who has religious faith	an additional dose that makes sure the first dose was effective
a supporter who accepts something as true	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.