endorser vs booster

endorser and booster both are nouns.

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

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

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

endorser (noun)	booster (noun)
someone who expresses strong approval	an additional dose that makes sure the first dose was effective
a person who transfers his ownership interest in something by signing a check or negotiable security	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.