Pin·ion, n.
 1. A feather; a quill.
 2. A wing, literal or figurative.
    Swift on his sooty pinions flits the gnome.   --Pope.
 3. The joint of bird's wing most remote from the body.
 4. A fetter for the arm.
 5. Mech. A cogwheel with a small number of teeth, or leaves, adapted to engage with a larger wheel, or rack (see Rack); esp., such a wheel having its leaves formed of the substance of the arbor or spindle which is its axis.
 Lantern pinion. See under Lantern.
 Pinion wire, wire fluted longitudinally, for making the pinions of clocks and watches. It is formed by being drawn through holes of the shape required for the leaves or teeth of the pinions.