booster vs booster shot

booster and booster shot both are nouns.

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

As nouns, booster and booster shot are synonyms defined as:

booster and booster shot: an additional dose that makes sure the first dose was effective

Other synonyms of booster include booster dose, recall dose.

booster (noun)	booster shot (noun)
an additional dose that makes sure the first dose was effective	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.