master vs principal

master and principal both are nouns.

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

As adjectives, master and principal are synonyms defined as:

Other synonyms of master include chief, main, primary.

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

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

master (noun)	principal (noun)
an original creation (i.e., an audio recording) from which copies can be made	the educator who has executive authority for a school
key that secures entrance everywhere	an actor who plays a principal role
an artist of consummate skill	the major party to a financial transaction at a stock exchange; buys and sells for his own account
a combatant who is able to defeat rivals	(criminal law) any person involved in a criminal offense, regardless of whether the person profits from such involvement
an authority qualified to teach apprentices	the original amount of a debt on which interest is calculated
directs the work of others	capital as contrasted with the income derived from it
a person who has general authority over others
someone who holds a master's degree from academic institution
presiding officer of a school
an officer who is licensed to command a merchant ship

master (adjective)	principal (adjective)
most important element	most important element

master (verb)	principal (verb)
have a firm understanding or knowledge of; be on top of
be or become completely proficient or skilled in
get on top of; deal with successfully
have dominance or the power to defeat over