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