dosage vs booster

dosage and booster both are nouns.

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

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

dosage (noun)	booster (noun)
a measured portion of medicine taken at any one time	an additional dose that makes sure the first dose was effective
the quantity of an active agent (substance or radiation) taken in or absorbed at any one time	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.