1. Also called incidence . Optics, Physics. the angle that a straight line, ray of light, etc., meeting a surface, makes with a normal to the surface at the point of meeting.
2. (on an airplane) the angle, usually fixed, between a wing or tail root chord and the axis of the fuselage.
3. Chiefly Brit. See angle of attack (def. 1).
[ 1620-30 ]