The Collaborative International Dictionary of English v.0.48:

occupied \occupied\ adj.
   1. Engaged; in use; being used by a person and not free for
      use by someone else; as, the wc is occupied. Opposite of
      free, available, and unoccupied.
      [WordNet 1.5]

   2. Inhabited, lived-in, tenanted; having residents; -- of
      dwelling units. [Narrower terms: owner-occupied] WordNet
      1.5]

   3. Overrun, taken over; -- of countries or territories; as,
      occupied France. Opposite of unoccupied.
      [WordNet 1.5]

   4. Busy; actively or fully engaged in some activity; -- of
      people. Opposite of idle.

   Syn: employed, engaged.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Occupy \Oc"cu*py\, v. t. [imp. & p. p. Occupied; p. pr. & vb.
   n. Occupying.] [OE. occupien, F. occuper, fr.L. occupare;
   ob (see Ob-) + a word akin to capere to take. See
   Capacious.]
   1. To take or hold possession of; to hold or keep for use; to
      possess.
      [1913 Webster]

            Woe occupieth the fine [end] of our gladness.
                                                  --Chaucer.
      [1913 Webster]

            The better apartments were already occupied. --W.
                                                  Irving.
      [1913 Webster]

   2. To hold, or fill, the dimensions of; to take up the room
      or space of; to cover or fill; as, the camp occupies five
      acres of ground. --Sir J. Herschel.
      [1913 Webster]

   3. To possess or use the time or capacity of; to engage the
      service of; to employ; to busy.
      [1913 Webster]

            An archbishop may have cause to occupy more
            chaplains than six.                   --Eng. Statute
                                                  (Hen. VIII. )
      [1913 Webster]

            They occupied themselves about the Sabbath. --2
                                                  Macc. viii.
                                                  27.
      [1913 Webster]

   4. To do business in; to busy one's self with. [Obs.]
      [1913 Webster]

            All the ships of the sea, with their mariners, were
            in thee to occupy the merchandise.    --Ezek. xxvii.
                                                  9.
      [1913 Webster]

            Not able to occupy their old crafts.  --Robynson
                                                  (More's
                                                  Utopia).
      [1913 Webster]

   5. To use; to expend; to make use of. [Obs.]
      [1913 Webster]

            All the gold that was occupied for the work. --Ex.
                                                  xxxviii. 24.
      [1913 Webster]

            They occupy not money themselves.     --Robynson
                                                  (More's
                                                  Utopia).
      [1913 Webster]

   6. To have sexual intercourse with. [Obs.] --Nares.
      [1913 Webster]

WordNet (r) 3.0 (2006):

occupied
    adj 1: held or filled or in use; "she keeps her time well
           occupied"; "the wc is occupied" [ant: unoccupied]
    2: seized and controlled as by military invasion; "the occupied
       countries of Europe" [ant: unoccupied]
    3: resided in; having tenants; "not all the occupied (or
       tenanted) apartments were well kept up" [syn: occupied,
       tenanted]
    4: having ones attention or mind or energy engaged; "she keeps
       herself fully occupied with volunteer activities"; "deeply
       engaged in conversation" [syn: engaged, occupied]

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "occupied":
   absorbed, absorbed in, abstracted, at it, at work, buried in,
   buried in thought, busy, caught up in, colonized, contemplating,
   contemplative, devoted, devoted to, empeopled, employed, engaged,
   engaged in thought, engrossed, engrossed in, engrossed in thought,
   full of business, hard at it, hard at work, immersed in,
   immersed in thought, in harness, inhabited, intent, intent on,
   introspective, involved, lost in, lost in thought, meditating,
   meditative, monomaniacal, monopolized, obsessed, on duty,
   on the go, on the hop, on the job, on the jump, on the move,
   on the run, peopled, populated, populous, preoccupied, rapt,
   settled, single-minded, studious, studying, submerged in, swept up,
   taken up with, tenanted, tied up, totally absorbed, working,
   wrapped in, wrapped in thought, wrapped up in