Prin″ci‐pal (?), a. [F., from L. principalis. See Prince.] 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. Spenser.
Principal axis. See Axis of a curve, under Axis. — Principal axes of a quadric(Geom.), three lines in which the principal planes of the solid intersect two and two, as in an ellipsoid. — Principal challenge. (Law) See under Challenge. — Principal plane. See Plane of projection (a), under Plane. — Principal of a quadric(Geom.), 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(Persp.), the projection of the point of sight upon the plane of projection. — Principal ray(Persp.), the line drawn through the point of sight perpendicular to the perspective plane. — Principal section(Crystallog.), a plane passing through the optical axis of a crystal.