The Collaborative International Dictionary of English v.0.48:

Vacation \Va*ca"tion\, n. [F., fr. L. vacatio a being free from
   a duty, service, etc., fr. vacare. See Vacate.]
   [1913 Webster]
   1. The act of vacating; a making void or of no force; as, the
      vacation of an office or a charter.
      [1913 Webster]

   2. Intermission of a stated employment, procedure, or office;
      a period of intermission; rest; leisure.
      [1913 Webster]

            It was not in his nature, however, at least till
            years had chastened it, to take any vacation from
            controversy.                          --Palfrey.
      [1913 Webster] Hence, specifically:
      [1913 Webster]
      (a) (Law) Intermission of judicial proceedings; the space
          of time between the end of one term and the beginning
          of the next; nonterm; recess. "With lawyers in the
          vacation." --Shak.
          [1913 Webster]
      (b) A period of intermission of regular paid work or
          employment, or of studies and exercises at an
          educational institution; the time during which a
          person temporarily ceases regular duties of any kind
          and performs other activites, usually some form of
          liesure; holidays; recess (at a school); as, the
          spring vacation; to spend one's vacation travelling;
          to paint the house while on vacation. Vacation is
          typically used for rest, travel, or recreation, but
          may be used for any purpose. In Britain this sense of
          vacation is usually referred to as holiday.
          [1913 Webster +PJC]
      (c) The time when an office is vacant; esp. (Eccl.), the
          time when a see, or other spiritual dignity, is
          vacant.
          [1913 Webster]

WordNet (r) 3.0 (2006):

vacation
    n 1: leisure time away from work devoted to rest or pleasure;
         "we get two weeks of vacation every summer"; "we took a
         short holiday in Puerto Rico" [syn: vacation, holiday]
    2: the act of making something legally void
    v 1: spend or take a vacation [syn: vacation, holiday]

Moby Thesaurus II by Grady Ward, 1.0:

117 Moby Thesaurus words for "vacation":
   AWOL, Christmas, French leave, Sunday, abeyance, abolishment,
   abolition, abrogation, abscondence, absence, absence without leave,
   absentation, absenteeism, absenting, annulment, break,
   breathing space, caesura, cancel, canceling, cancellation,
   cassation, cease-fire, coffee break, countermand, counterorder,
   cut, day off, default, defeasance, departure, disappearance,
   downtime, drop, escape, excused absence, fleeing, furlough,
   go on furlough, go on leave, half time, half-time intermission,
   hesitation, holiday, hooky, interim, interlude, intermezzo,
   intermission, intermittence, interregnum, interruption, interval,
   invalidation, lapse, layoff, leave, leave of absence, leaving,
   letup, liberty, lull, make holiday, nonappearance, nonattendance,
   nullification, off-time, paid holiday, paid vacation, pause,
   plateau, point of repose, quiet spell, recall, recantation, recess,
   relief, remission, renege, repeal, rescinding, rescindment,
   rescission, respite, rest, resting point, retraction, reversal,
   revocation, revoke, revokement, running away, sabbatical,
   sabbatical leave, sabbatical year, setting aside, shore leave,
   sick leave, stand-down, stay, suspension, take a holiday,
   take leave, time off, time out, truancy, truantism, truce,
   unexcused absence, vacatur, voidance, voiding, waiver, waiving,
   weekend, withdrawal, write-off