weathercock

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A weathervane, especially one in the form of a rooster.
• noun One that is very changeable or fickle.
• intransitive verb To have a tendency to veer in the direction of the wind. Used of an aircraft or a missile.

from The Century Dictionary.

• To serve as a weathercock to or on.
• noun A vane or weather-vane; a pointing device, set on the top of a spire or other elevation, and turning with the wind, thus showing its direction. See cut under vane.
• noun Figuratively, any thing or person that is easily and frequently turned or swayed; a fickle or inconstant person.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To supply with a weathercock; to serve as a weathercock for.
• noun A vane, or weather vane; -- so called because originally often in the figure of a cock, turning on the top of a spire with the wind, and showing its direction.
• noun Hence, any thing or person that turns easily and frequently; one who veers with every change of current opinion; a fickle, inconstant person.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun US A weather vane in the shape of a cockerel.
• verb intransitive, of a boat To turn upwind because of the difference in water pressure on two sides.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun weathervane with a vane in the form of a rooster