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. Principal axis. See Axis of a curve, under Axis. Principal axes of a quadric, a plane passing through the optical axis of a crystal.
Origin: F, from L. Principalis. See Prince.