The Collaborative International Dictionary of English v.0.48:

Vacancy \Va"can*cy\, n.; pl. Vacancies. [Cf. F. vacance.]
   [1913 Webster]
   1. The quality or state of being vacant; emptiness; hence,
      freedom from employment; intermission; leisure; idleness;
      listlessness.
      [1913 Webster]

            All dispositions to idleness or vacancy, even before
            they are habits, are dangerous.       --Sir H.
                                                  Wotton.
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   2. That which is vacant. Specifically:
      [1913 Webster]
      (a) Empty space; vacuity; vacuum.
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                How is't with you,
                That you do bend your eye on vacancy? --Shak.
          [1913 Webster]
      (b) An open or unoccupied space between bodies or things;
          an interruption of continuity; chasm; gap; as, a
          vacancy between buildings; a vacancy between sentences
          or thoughts.
          [1913 Webster]
      (c) Unemployed time; interval of leisure; time of
          intermission; vacation.
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                Time lost partly in too oft idle vacancies given
                both to schools and universities. --Milton.
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                No interim, not a minute's vacancy. --Shak.
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                Those little vacancies from toil are sweet.
                                                  --Dryden.
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      (d) A place or post unfilled; an unoccupied office; as, a
          vacancy in the senate, in a school, etc.
          [1913 Webster]

WordNet (r) 3.0 (2006):

vacancy
    n 1: being unoccupied
    2: an empty area or space; "the huge desert voids"; "the
       emptiness of outer space"; "without their support he'll be
       ruling in a vacuum" [syn: void, vacancy, emptiness,
       vacuum]

Moby Thesaurus II by Grady Ward, 1.0:

88 Moby Thesaurus words for "vacancy":
   absence, absence of mind, appointment, bareness, barrenness, berth,
   billet, blank, blank mind, blankmindedness, blankness, bleakness,
   breach, calm of mind, deficiency, deprivation, desertedness,
   desolateness, employment, emptiness, emptiness of mind,
   empty-headedness, engagement, fallow mind, fatuity, foolishness,
   gap, gig, hiatus, hollowness, inanition, inanity, incomprehension,
   incumbency, jejunity, job, lacuna, mental blankness, mental void,
   moonlighting, negation, negativeness, negativity, nihility,
   nirvana, nonbeing, nonentity, nonexistence, noninhabitance,
   nonoccupance, nonoccupancy, nonoccurrence, nonreality,
   nonresidence, nonsubsistence, not-being, nothingness, nullity,
   oblivion, office, opening, passivity, place, place open, position,
   post, quietism, second job, service, situation, slot, station,
   tabula rasa, tenure, thoughtfreeness, thoughtlessness,
   tranquillity, unactuality, unawareness, unintelligence, unreality,
   vacant post, vacuity, vacuousness, vacuum, vapidity, void,
   voidness



Bouvier's Law Dictionary, Revised 6th Ed (1856):

VACANCY. A place which is empty. The term is principally applied to cases
where an office is not filled.
     2. By the constitution of the United States, the president has the
power to fill up vacancies that may happen during the recess of the senate.
Whether the president can create an office and fill it during the recess of
the senate, seems to have been much questioned. Story, Const. Sec. 1553. See
Serg. Const. Law, ch. 31; 1 Breese, R. 70.