Meaning of windage

wind•age

1. the influence of the wind in deflecting a missile.
2. the amount of such deflection.
3. the degree to which a gunsight must be adjusted to correct for windage.
4. a difference between the diameter of a projectile and that of the gun bore, for the escape of gas and the prevention of friction.
5. that portion of a vessel's surface upon which the wind acts.
6. friction between a rotor and the air within its casing, as in an electric generator.
7. the resisting influence of air against the rotating armature of a dynamo, creating a power loss.