Source : Webster's Revised Unabridged Dictionary (1913)

Justify \Jus"ti*fy\, v. t. [imp. & p. p. {Justified}; p. pr. &
   vb. n. {Justifying}.] [F. justifier, L. justificare; justus
   just + -ficare (in comp.) to make. See {Just}, a., and
   {-fy}.]
   1. To prove or show to be just; to vindicate; to maintain or
      defend as conformable to law, right, justice, propriety,
      or duty.

            That to the height of this great argument I may
            assert eternal providence, And justify the ways of
            God to men.                           --Milton.

            Unless the oppression is so extreme as to justify
            revolution, it would not justify the evil of
            breaking up a government.             --E. Everett.

   2. To pronounce free from guilt or blame; to declare or prove
      to have done that which is just, right, proper, etc.; to
      absolve; to exonerate; to clear.

            I can not justify whom the law condemns. --Shak.

   3. (Theol.) To treat as if righteous and just; to pardon; to
      exculpate; to absolve.

            By him all that believe are justified from all
            things, from which ye could not be justified by the
            law of Moses.                         --Acts xiii.
                                                  39.

   4. To prove; to ratify; to confirm. [Obs.] --Shak.

   5. (Print.) To make even or true, as lines of type, by proper
      spacing; to adjust, as type. See {Justification}, 4.

   Syn: To defend; maintain; vindicate; excuse; exculpate;
        absolve; exonerate.

Justify \Jus"ti*fy\, v. i.
   1. (Print.) To form an even surface or true line with
      something else; to fit exactly.

Justify \Jus"ti*fy\, v. t. (Law)
   (a) To show (a person) to have had a sufficient legal reason
       for an act that has been made the subject of a change or
       accusation.
   (b) To qualify (one's self) as a surely by taking oath to the
       ownership of sufficient property.

             The production of bail in court, who there justify
             themselves against the exception of the plaintiff.
                                                  --Bouvier's
                                                  Law Dict.

Source : WordNet®

justify
     v 1: show to be reasonable or provide adequate ground for; "The
          emergency does not warrant all of us buying guns"; "The
          end justifies the means" [syn: {warrant}]
     2: show to be right by providing justification or proof;
        "vindicate a claim" [syn: {vindicate}]
     3: defend, explain, clear away, or make excuses for by
        reasoning; "rationalize the child's seemingly crazy
        behavior"; "he rationalized his lack of success" [syn: {apologize},
         {apologise}, {excuse}, {rationalize}, {rationalise}]
     4: let off the hook; "I absolve you from this responsibility"
        [syn: {absolve}, {free}] [ant: {blame}]
     5: adjust the spaces between words; "justify the margins"
     [also: {justified}]