The Collaborative International Dictionary of English v.0.48:

Abjuration \Ab`ju*ra"tion\, n. [L. abjuratio: cf. F.
   abjuration.]
   1. The act of abjuring or forswearing; a renunciation upon
      oath; as, abjuration of the realm, a sworn banishment, an
      oath taken to leave the country and never to return.
      [1913 Webster]

   2. A solemn recantation or renunciation; as, an abjuration of
      heresy.
      [1913 Webster]

   Oath of abjuration, an oath asserting the right of the
      present royal family to the crown of England, and
      expressly abjuring allegiance to the descendants of the
      Pretender. --Brande & C.
      [1913 Webster]

WordNet (r) 3.0 (2006):

abjuration
    n 1: a disavowal or taking back of a previous assertion [syn:
         retraction, abjuration, recantation]

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "abjuration":
   abandonment, abdication, abeyance, abjurement, abrogation,
   absolute contradiction, annulment, cessation, cession, chucking,
   chucking out, cold storage, contempt, contradiction,
   contrary assertion, contravention, controversion, countering,
   crossing, declination, declining, denial, desistance, despisal,
   despising, disaffirmation, disallowance, disapproval, disavowal,
   discard, disclaimer, disclamation, discontinuance, discounting,
   dismissal, disowning, disownment, dispensation, disposal,
   disposition, disproof, disregard, dropping out, dumping, exception,
   exclusion, expatriation, forbearance, forgoing, forswearing,
   gainsaying, getting rid of, giving up, handing over, ignoring,
   impugnment, letting go, nonacceptance, nonapproval,
   nonconsideration, nonexercise, nullification, palinode, palinody,
   passing by, putting away, putting out, rebuff, recantation,
   refusal, refutation, rejection, release, relinquishment, reneging,
   renouncement, renunciation, repudiation, repulse, resignation,
   retractation, retraction, revocation, revokement, riddance,
   sacrifice, scouting, spurning, surrender, suspension, swearing off,
   throwing out, turning out, unsaying, waiver, withdrawal,
   withdrawing, yielding



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

ABJURATION. 1. A renunciation of allegiance to a country by oath.
     2.-1. The act of Congress of the 14th of April, 1802, 2 Story's Laws,
U.S. 850, requires that when an alien shall apply to be admitted a citizen
of the United States, he shall declare on oath or affirmation before the
court where the application shall be made, inter alia, that he doth
absolutely and entirely renounce and abjure all allegiance and fidelity
which he owes to any foreign prince, &c., and particularly, by name, the
prince, &c., whereof he was before a citizen or subject. Rawle on the Const.
98.
     3.-2. In England the oath of abjuration is an oath by which an
Englishman binds himself not to acknowledge any right in the Pretender to
the throne of England.
     4.-3  It signifies also, according to 25 Car. H., an oath abjuring to
certain doctrines of the church of Rome.
     5.-4. In the ancient English law it was a renunciation of one's
country and taking an oath of perpetual banishment. A man who had committed
a felony, and for safety flea to a sanctuary might within forty days'
confess the fact, and take the oath of abjuration and perpetual banishment;
he was then transported.  This was abolished by Stat. 1 Jac. 1, c. 25. Ayl.
Parerg. 14.