principal : Idioms & Phrases

• (Geom.), three lines in which the principal planes of the solid intersect two and two, as in an ellipsoid.

Webster 1913

• noun a line that passes through the center of curvature of a lens so that light is neither reflected nor refracted
  optic axis.
  
  • in a normal eye the optic axis is the direction in which objects are seen most distinctly

WordNet

• . See Axis of a curve, under Axis.

Webster 1913

• . (Law) See under Challenge.

Webster 1913

• noun the diagonal of a square matrix running from the upper left entry to the lower right entry
  main diagonal.
  

WordNet

• noun the scientist in charge of an experiment or research project
  PI.
  

WordNet

• (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.

Webster 1913

• . See Plane of projection (a), under Plane.

Webster 1913

• (Persp.), the projection of the point of sight upon the plane of projection.

Webster 1913

• (Persp.), the line drawn through the point of sight perpendicular to the perspective plane.

Webster 1913

• (Crystallog.), a plane passing through the optical axis of a crystal.

Webster 1913

• noun capital as contrasted with the income derived from it
  corpus; principal.
  

WordNet

• noun the educator who has executive authority for a school
  head; head teacher; principal.
  
  • she sent unruly pupils to see the principal

WordNet