headmaster vs principal

headmaster and principal both are nouns.

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

As nouns, principal is a hypernym of headmaster; that is, principal is a word with a broader meaning than headmaster:

Other hypernyms of headmaster include adult male, man, head, head teacher, school principal.

headmaster (noun)	principal (noun)
presiding officer of a school	the educator who has executive authority for 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

headmaster (adjective)	principal (adjective)
	most important element