The Collaborative International Dictionary of English v.0.48:

Unjust \Un*just"\, a.
   1. Acting contrary to the standard of right; not animated or
      controlled by justice; false; dishonest; as, an unjust man
      or judge.
      [1913 Webster]

   2. Contrary to justice and right; prompted by a spirit of
      injustice; wrongful; as, an unjust sentence; an unjust
      demand; an unjust accusation.
      [1913 Webster] -- Un*just"ly, adv. -- Un*just"ness, n.
      [1913 Webster]

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

UNJUST. That which is done against the perfect rights of another; that which
is against the established law; that which is opposed to a law which is the
test of right and wrong. 1 Toull. tit. prel. n. 5; Aust. Jur. 276, n.; Hein.
Lec. El. Sec. 1080.