The retarding force of air friction on a moving object

• The deflection of a projectile resulting from the effects of wind
• Exposure to the wind (as the exposed part of a vessel's hull which is responsible for wind resistance)
• Bore-to-projectile difference in diameter
• Archer's concern

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Windage \Wind"age\, n. [From Wind air in motion.] (Gun.) The difference between the diameter of the bore of a gun and that of the shot fired from it. The sudden compression of the air caused by a projectile in passing close to another body.

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1710, "allowance of space between the projectile and the diameter of the tube of a firearm," from wind (n.1) + -age . Meaning "allowance for wind deflection" is from 1867.

Wikipedia Word definitions in Wikipedia
Windage is a force created on an object by friction when there is relative movement between air and the object. There are two causes of windage: The object is moving and being slowed by resistance from the air. A wind is blowing producing a force on the ...

WordNet Word definitions in WordNet
n. the retarding force of air friction on a moving object bore-to-projectile difference in diameter exposure to the wind (as the exposed part of a vessel's hull which is responsible for wind resistance) [syn: wind exposure ] the deflection of a projectile ...

Wiktionary Word definitions in Wiktionary
n. 1 (context automotive English) drag on the crankshaft caused by oil splashing out of the sump when rotating at high speeds. 2 (context ballistics English) The difference in diameter between the bore of a firearm and the shot 3 (context ballistics English) ...