Source : Webster's Revised Unabridged Dictionary (1913)

Vacant \Va"cant\, a. [F., fr. L. vacans, -antis, p. pr. of
   vacare to be empty, to be free or unoccupied, to have
   leisure, also vocare; akin to vacuus empty, and probably to
   E. void. Cf. {Evacuate}, {Void}, a.]
   1. Deprived of contents; not filled; empty; as, a vacant
      room.

            Stuffs out his vacant garments with his form.
                                                  --Shak.

            Being of those virtues vacant.        --Shak.

            There is no fireside, howsoe'er defended, But has
            one vacant chair.                     --Longfellow.

   2. Unengaged with business or care; unemployed; unoccupied;
      disengaged; free; as, vacant hours.

            Religion is the interest of all; but philosophy of
            those . . . at leisure, and vacant from the affairs
            of the world.                         --Dr. H. More.

            There was not a minute of the day which he left
            vacant.                               --Bp. Fell.

   3. Not filled or occupied by an incumbent, possessor, or
      officer; as, a vacant throne; a vacant parish.

            Special dignities which vacant lie For thy best use
            and wearing.                          --Shak.

   4. Empty of thought; thoughtless; not occupied with study or
      reflection; as, a vacant mind.

            The duke had a pleasant and vacant face. --Sir H.
                                                  Wotton.

            When on my couch I lie In vacant or in pensive mood.
                                                  --Wordsworth.

   5. (Law) Abandoned; having no heir, possessor, claimant, or
      occupier; as, a vacant estate. --Bouvier.

   {Vacant succession} (Law), one that is claimed by no person,
      or where all the heirs are unknown, or where all the known
      heirs to it have renounced it. --Burrill.

   Syn: Empty; void; devoid; free; unemployed; disengaged;
        unincumbered; uncrowded; idle.

   Usage: {Vacant}, {Empty}. A thing is empty when there is
          nothing in it; as, an empty room, or an empty noddle.
          Vacant adds the idea of having been previously filled,
          or intended to be filled or occupied; as, a vacant
          seat at table; a vacant office; vacant hours. When we
          speak of a vacant look or a vacant mind, we imply the
          absence of the intelligence naturally to be expected
          there.

Source : WordNet®

vacant
     adj 1: void of thought or knowledge; "a vacant mind"
     2: without an occupant or incumbent; "the throne is never
        vacant"