commander

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

• noun A person who commands, especially a commanding officer.
• noun A commissioned rank in the US Navy or Coast Guard that is above lieutenant commander and below captain.
• noun One who holds this rank.
• noun The chief commissioned officer of a military unit regardless of his or her rank.
• noun An officer in some knightly or fraternal orders.

from The Century Dictionary.

• noun One who has the authority or power to command or order; especially, a military leader; the chief officer of an army or of any division of it.
• noun Hence One who has control, in any sense.
• noun Specifically In the British and United States navies, an officer next in rank below a captain and above a lieutenant or a lieutenant-commander.
• noun The chief officer of a commandery in the medieval orders of Knights Hospitallers, Templars, etc. See commandery, 2 .
• noun A similar officer in certain secret orders, as in the American order of Knights Templars.
• noun A member of a higher class in a modern honorary order.
• noun A heavy beetle or wooden mallet used in paving, or by sailmakers and riggers.
• noun In surgery, a box or cradle for incasing an injured limb.
• noun In hat-making, a string which is pressed down over a conical hat while it is on the block, to bring it to the required cylindrical form.
• noun In medieval fortification, same as cavalier, 5.
• noun A member of the highest class, or one of the highest classes, of some modern honorary orders. See order. Synonyms Leader, Head, etc. See chief.

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

• noun A chief; one who has supreme authority; a leader; the chief officer of an army, or of any division of it.
• noun (Navy) An officer who ranks next below a captain, -- ranking with a lieutenant colonel in the army.
• noun The chief officer of a commandery.
• noun A heavy beetle or wooden mallet, used in paving, in sail lofts, etc.
• noun the military title of the officer who has supreme command of the land or naval forces or the united forces of a nation or state; a generalissimo. .

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

• noun One who exercises control and direction of a military or naval organization.
• noun A naval officer whose rank is above that of a lieutenant commander and below that of captain.
• noun One who exercises control and direction over a group of persons.
• noun A designation or rank in certain non-military organizations such as NASA and various police forces.
• noun obsolete The chief officer of a commandry.
• noun A heavy beetle or wooden mallet, used in paving, in sail lofts, etc.

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

• noun an officer in command of a military unit
• noun an officer in the airforce
• noun a commissioned naval officer who ranks above a lieutenant commander and below a captain
• noun someone in an official position of authority who can command or control others