justify  verb [T]
 to give or to be a good reason for
 I can't really justify taking another day off work [+ v-ing]
 I hope you're able to justify yourself/your actions (=give a good
 reason for what you have done).
 These recommendations will need to be justified to the committee
 before they can be implemented.
 The results of the study have certainly justified the money that was
 spent on it.
 Are you sure that these measures are justified?
 I'm sure I'll be able to justify your faith in me (=will be able to do
 what you expect me to do).

 justifiable   adjective
 Her actions were quite justifiable (=there was a good reason for them)
 in the circumstances.
 Could it ever be justifiable to use atomic weapons against towns and
 cities?

 (American) Justifiable homicide is an act of killing someone, esp. in
 self-defence, which is considered to be lawful.

 justifiably   adverb
 He was justifiably proud of his achievements.

 justification  noun [U]
 We expect you to provide a justification of/for (=an acceptable
 explanation for) your actions. [C]
 It can be said, with some justification (=There is good reason to say),
 that she is one of the greatest actresses on the English stage
 today. [U]

 justified  adjective
 I accept that the criticism is completely justified (=there is a good
 reason for it).
 I think you were quite justified in (=had a good reason to)
 complaining.