of import vs principal

of import is not a noun while principal is a noun.

Word	Noun	Adjective	Verb	Adverb
of import	No	Yes	No	No
principal	Yes	Yes	No	No

of import (noun)	principal (noun)
	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

of import (adjective)	principal (adjective)
of great significance or value	most important element