- 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.
- One of the metal guidance or stabilizing fins attached to the tail of a bomb or other missile.
- (countable) A weather vane.
- A sight on a sextant or compass.
- (ornithology) The flattened, web-like part of a feather, consisting of a series of barbs on either side of the shaft.