principal vs headmaster

principal and headmaster both are nouns.

Word	Noun	Adjective	Verb	Adverb
principal	Yes	Yes	No	No
headmaster	Yes	No	No	No

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

Other hyponyms of principal include chancellor, master, schoolmaster, headmistress.

principal (noun)	headmaster (noun)
the educator who has executive authority for a school	presiding officer of a school
an actor who plays a principal role
the major party to a financial transaction at a stock exchange; buys and sells for his own account
(criminal law) any person involved in a criminal offense, regardless of whether the person profits from such involvement
the original amount of a debt on which interest is calculated
capital as contrasted with the income derived from it

principal (adjective)	headmaster (adjective)
most important element