Of·fi·cer n.
 1. One who holds an office; a person lawfully invested with an office, whether civil, military, or ecclesiastical; as, a church officer; a police officer; a staff officer. “I am an officer of state.”
 2. U. S. Mil. Specifically, a commissioned officer, in distinction from a warrant officer or an enlisted man.
 Field officer, General officer, etc. See under Field, General. etc.
 Officer of the day Mil., the officer who, on a given day, has charge for that day of the guard, prisoners, and police of the post or camp; abbreviated O. D., OD, or O. O. D.
 Officer of the deck, or Officer of the watch Naut., the officer temporarily in charge on the deck of a vessel, esp. a war vessel.