The Collaborative International Dictionary of English v.0.48:

Vacate \Va"cate\, v. t. [imp. & p. p. Vacated; p. pr. & vb. n.
   Vacating.] [L. vacare, vacatum, to be empty. See Vacant.]
   1. To make vacant; to leave empty; to cease from filling or
      occupying; as, it was resolved by Parliament that James
      had vacated the throne of England; the tenant vacated the
      house.
      [1913 Webster]

   2. To annul; to make void; to deprive of force; to make of no
      authority or validity; as, to vacate a commission or a
      charter; to vacate proceedings in a cause.
      [1913 Webster]

            That after act vacating the authority of the
            precedent.                            --Eikon
                                                  Basilike.
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            The necessity of observing the Jewish Sabbath was
            vacated by the apostolical institution of the Lord's
            Day.                                  --R. Nelson.
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   3. To defeat; to put an end to. [R.]
      [1913 Webster]

            He vacates my revenge.                --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vacate
    v 1: leave (a job, post, or position) voluntarily; "She vacated
         the position when she got pregnant"; "The chairman resigned
         when he was found to have misappropriated funds" [syn:
         vacate, resign, renounce, give up]
    2: leave behind empty; move out of; "You must vacate your office
       by tonight" [syn: vacate, empty, abandon]
    3: cancel officially; "He revoked the ban on smoking"; "lift an
       embargo"; "vacate a death sentence" [syn: revoke, annul,
       lift, countermand, reverse, repeal, overturn,
       rescind, vacate]

Moby Thesaurus II by Grady Ward, 1.0:

107 Moby Thesaurus words for "vacate":
   abandon, abdicate, abjure, abolish, abrogate, abscond, annul,
   back out, be pensioned, be superannuated, beat a retreat, beg off,
   bow out, cancel, cede, clear, countermand, counterorder, cry off,
   demit, depart from, desert, disannul, disappear, discard,
   discharge, disgorge, dispense with, dispose of, dissolve,
   do away with, do without, drop, drop out, dump, empty, evacuate,
   forgo, forsake, forswear, get along without, get out of,
   get rid of, give away, give up, go back on, have done with,
   invalidate, jettison, jilt, kiss good-bye, leave, leave behind,
   leave flat, let go, make a sacrifice, make void, maroon, nullify,
   override, overrule, part with, pension off, pull out, quash, quit,
   quit cold, quitclaim, recall, recant, relinquish, remove,
   render up, renege, renounce, renounce the throne, repeal,
   repudiate, rescind, resign, retire, retire from office, retract,
   retreat, reverse, revoke, sacrifice, say goodbye to, set aside,
   spare, stand aside, stand down, step aside, superannuate,
   surrender, suspend, swear off, take leave of, throw over, throw up,
   vanish, void, waive, withdraw, withdraw from, write off, yield