an'gle of in'cidence
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).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.