booster vs endorser

booster and endorser both are nouns.

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

As nouns, endorser is a hyponym of booster; that is, endorser is a word with a more specific, narrower meaning than booster:

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