The Collaborative International Dictionary of English v.0.48:

Abdicate \Ab"di*cate\, v. t. [imp. & p. p. Abdicated; p. pr. &
   vb. n. Abdicating.] [L. abdicatus, p. p. of abdicare; ab +
   dicare to proclaim, akin to dicere to say. See Diction.]
   1. To surrender or relinquish, as sovereign power; to
      withdraw definitely from filling or exercising, as a high
      office, station, dignity; as, to abdicate the throne, the
      crown, the papacy.
      [1913 Webster]

   Note: The word abdicate was held to mean, in the case of
         James II., to abandon without a formal surrender.
         [1913 Webster]

               The cross-bearers abdicated their service.
                                                  --Gibbon.
         [1913 Webster]

   2. To renounce; to relinquish; -- said of authority, a trust,
      duty, right, etc.
      [1913 Webster]

            He abdicates all right to be his own governor.
                                                  --Burke.
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            The understanding abdicates its functions. --Froude.
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   3. To reject; to cast off. [Obs.] --Bp. Hall.
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   4. (Civil Law) To disclaim and expel from the family, as a
      father his child; to disown; to disinherit.
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   Syn: To give up; quit; vacate; relinquish; forsake; abandon;
        resign; renounce; desert.

   Usage: To Abdicate, Resign. Abdicate commonly expresses
          the act of a monarch in voluntary and formally
          yielding up sovereign authority; as, to abdicate the
          government. Resign is applied to the act of any
          person, high or low, who gives back an office or trust
          into the hands of him who conferred it. Thus, a
          minister resigns, a military officer resigns, a clerk
          resigns. The expression, "The king resigned his
          crown," sometimes occurs in our later literature,
          implying that he held it from his people. -- There are
          other senses of resign which are not here brought into
          view.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Abdicate \Ab"di*cate\, v. i.
   To relinquish or renounce a throne, or other high office or
   dignity.
   [1913 Webster]

         Though a king may abdicate for his own person, he
         cannot abdicate for the monarchy.        --Burke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

abdicate
    v 1: give up, such as power, as of monarchs and emperors, or
         duties and obligations; "The King abdicated when he married
         a divorcee" [syn: abdicate, renounce]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "abdicate":
   abandon, abjure, acknowledge defeat, be pensioned,
   be superannuated, cashier, cast, cease, cede, cry quits, demit,
   desist from, drop, forgo, forswear, give over, give up, hand over,
   have done with, jettison, lay down, leave, leave off, pension off,
   quit, reject, relinquish, renounce, renounce the throne, resign,
   retire, retire from office, scrap, shed, slough, stand aside,
   stand down, step aside, superannuate, surrender, throw away,
   throw out, throw up, vacate, waive, withdraw from, wrest, yield