vane / vān/ • n. a broad blade attached to a rotating axis or wheel that pushes or is pushed by wind or water and forms part of a machine or device such as a windmill, propeller, or turbine. ∎ short for weathervane. ∎ the flat part on either side of the shaft of a feather. ∎ a broad, flat projecting surface designed to guide the motion of a projectile, such as a feather on an arrow or a fin on a torpedo. DERIVATIVES: vaned adj. [usu. in comb.] a three-vaned windmill.ORIGIN: late Middle English: dialect variant of obsolete fane ‘banner,’ of Germanic origin.