Principal — Defs

01 a. Highest in rank, authority, character, importance, or degree; most considerable or important; chief; main; as, the principal officers of a …

1.
Highest in rank, authority, character, importance, or degree; most considerable or important; chief; main; as, the principal officers of a Government; the principal men of a state; the principal productions of a country; the principal arguments in a case.
“Wisdom is the principal thing.” — Prov. iv. 7.
2.
Of or pertaining to a prince; princely.[A Latinism]

Phrases & compounds

Principal axis — See Axis of a curve, under Axis.

Principal axes of a quadric — three lines in which the principal planes of the solid intersect two and two, as in an ellipsoid.

Principal challenge — See under Challenge.

Principal plane — See Plane of projection (a), under Plane.

Principal of a quadric — three planes each of which is at right angles to the other two, and bisects all chords of the quadric perpendicular to the plane, as in an ellipsoid.

Principal point — the projection of the point of sight upon the plane of projection.

Principal ray — the line drawn through the point of sight perpendicular to the perspective plane.

Principal section — a plane passing through the optical axis of a crystal.

02 n. A leader, chief, or head; one who takes the lead; one who acts independently, or who has controlling authority or influence; as, the princi…

1.
A leader, chief, or head; one who takes the lead; one who acts independently, or 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.
2.
The chief actor in a crime, or an abettor who is present at it, -- as distinguished from an accessory.(Law)
3.
A thing of chief or prime importance; something fundamental or especially conspicuous.(Com.) [Obs.]