vane

noun

1. A weather vane
2. Any of several usually relatively thin, rigid, flat, or sometimes curved surfaces radially mounted along an axis, as a blade in a turbine or a sail on a windmill, that is turned by or used to turn a fluid
3. The flattened, web-like part of a feather, consisting of a series of barbs on either side of the shaft
4. A sight on a sextant or compass