Definition of "weathercock"

A weather vane, sometimes in the form of a cockerel.  examples

(figuratively) One who veers with every change of current opinion; a fickle, inconstant person.  examples

(chiefly Canada, US) A kind of wind pump whose top behaves like a weather vane, moving with the wind direction, but which also has a wheel attached to measure wind speed.  examples

(intransitive, of a boat) To turn upwind because of the difference in water pressure on two sides.  examples

(intransitive, of an airplane or missile) To veer into the direction of the oncoming (relative) wind.  examples

(transitive) To act as a weathercock for.  examples