principal vs of import

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

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

principal (noun)	of import (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

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