The Collaborative International Dictionary of English v.0.48:

Officer \Of"fi*cer\, n. [F. officier. See Office, and cf.
   Official, 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." --Shak.
      [1913 Webster]

   2. (U. S. Mil.) Specifically, a commissioned officer, in
      distinction from a warrant officer or an enlisted man.
      [1913 Webster]

   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Officer \Of"fi*cer\, v. t. [imp. & p. p. Officered; p. pr. &
   vb. n. Officering.]
   1. To furnish with officers; to appoint officers over.
      --Marshall.
      [1913 Webster]

   2. To command as an officer; as, veterans from old regiments
      officered the recruits.
      [1913 Webster]

WordNet (r) 3.0 (2006):

officer
    n 1: any person in the armed services who holds a position of
         authority or command; "an officer is responsible for the
         lives of his men" [syn: military officer, officer]
    2: someone who is appointed or elected to an office and who
       holds a position of trust; "he is an officer of the court";
       "the club elected its officers for the coming year" [syn:
       officeholder, officer]
    3: a member of a police force; "it was an accident, officer"
       [syn: policeman, police officer, officer]
    4: a person authorized to serve in a position of authority on a
       vessel; "he is the officer in charge of the ship's engines"
       [syn: officer, ship's officer]
    v 1: direct or command as an officer

Moby Thesaurus II by Grady Ward, 1.0:

161 Moby Thesaurus words for "officer":
   ADC, CO, G-man, John Law, MP, OD, administrator, aide,
   aide-de-camp, apparatchik, archon, bailiff, beadle, beagle,
   boatswain, bound bailiff, brigadier, brigadier general, bureaucrat,
   captain, catchpole, chancellor, chicken colonel, chief engineer,
   chief executive, chief executive officer, chief mate,
   chief of police, chief of staff, civil servant, colonel,
   commandant, commander, commander in chief, commanding officer,
   commissioned officer, commissioner, company officer, constable,
   cop, copper, dean, deck officer, deputy, deputy sheriff, detective,
   dick, dignitary, director, exec, executive, executive director,
   executive officer, executive secretary, fed, federal,
   field marshal, field officer, first lieutenant, five-star general,
   flic, four-star general, functionary, functionnaire, fuzz,
   gendarme, general, general officer, generalissimo, government man,
   inspector, jack-in-office, jemadar, junior officer, lawman, lictor,
   lieutenant, lieutenant colonel, lieutenant general, mace-bearer,
   magistrate, major, major general, management, manager,
   managing director, mandarin, marechal, marshal, master, mate,
   mounted policeman, narc, naval officer, navigating officer,
   navigator, office-bearer, officeholder, official, officiary,
   one-star general, orderly officer, patrolman, patron,
   peace officer, petty tyrant, pipes, placeman, police,
   police captain, police commissioner, police constable,
   police inspector, police matron, police officer, police sergeant,
   policeman, policewoman, portreeve, prefect, president, prexy,
   provost, public official, public servant, quartermaster,
   red-tapist, reeve, risaldar, roundsman, sailing master,
   second mate, secretary, senior officer, sergeant, sergeant at arms,
   shavetail, sheriff, shipmaster, sirdar, skipper, staff officer,
   subahdar, subaltern, sublieutenant, superintendent, tec,
   the Old Man, the administration, the brass, three-star general,
   tipstaff, tipstaves, top brass, treasurer, trooper,
   two-star general, vice-chancellor, vice-president, warden,
   watch officer