Definition of: windage

(win′dij) noun
1. The rush of air caused by the rapid passage of an object, as a projectile or a railway train.
2. Deflection of an object, as a bullet, from its natural course due to wind pressure.
3. In a muzzleloading rifled gun, the difference between the diameter of a projectile and the bore through which it is discharged; also, in a smoothbore gun, the space between the surface of the bore and the projectile.
4. Mech. The free air space between any moving piece and the socket or bore in which it travels.
5. A contusion caused by sudden compression of air due to the passing of gunshot nearby.
6. Naut. The surface offered to the wind by a vessel.