PRINCIPAL n.
r who has controlling authority or influence; as, the principal of a faction, a school, a firm, etc.; -- distinguished from a subordinate, abettor, auxiliary, or assistant.
PRO adv.
For, on, or in behalf of, the affirmative side; -- in contrast with Ant: con. Pro and con, for and against, on the affirmative and on the negative side; as, they debated the question pro and con; -- formerly used also as a verb. -- Pros and cons, the arguments or reasons on either side.