what is a vane
Definition of vane. 1  1a : a movable device attached to an elevated object (as a spire) for showing the direction of the windb : one that is changeable or inconstant. 2  2 : a thin flat or curved object that is rotated about an axis by a flow of fluid or that rotates to cause a fluid to flow or that redirects a flow of fluid the vanes of a windmill.