WINDAGE

'Windage' is a force created on an object by friction when there is relative movement between air and the object.
There are two possible causes of windage:
# the object is moving and being slowed by resistance from the air
# a wind is blowing producing a force on the object
The term can refer to :

★ either, the effect of the force, for example the deflection of a missile or an aircraft by a cross wind

★ or, the area and shape of the object that make it susceptible to friction, for example those parts of a boat that are exposed to the wind.
Aerodynamic streamlining can be used to reduce 'windage'.
There is a similar hydrodynamic effect to windage.
In firearms parlance, 'windage' refers to the side-to-side adjustment of a rifle's sight, used to change the horizontal component of the aiming point. (The up-down adjustment for the vertical component is the 'elevation'.) It can also refer to the difference in diameter between the bore and the shot, especially in muskets and cannons.