The Collaborative International Dictionary of English v.0.48:

Extrajudicial \Ex`tra*ju*di"cial\, a.
   Out of or beyond the power authority of a court or judge;
   beyond jurisdiction; not valid as a part of a judicial
   proceeding; as, extrajudicial oaths, judgments, etc., are
   null and void. -- Ex`tra*ju*di"cial*ly, adv.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

extrajudicial
    adj 1: beyond the usual course of legal proceedings; legally
           unwarranted; "an extrajudicial penalty"

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

EXTRAJUDICIAL. That which does not belong to the judge or his jurisdiction,
notwithstanding which he takes. cognizance of it. Extrajudicial judgments
and acts are absolutely void. Vide Coram non judice, and Merl. Repert. mots
Exces de Pouvoir.