Cameron stood in the House of Commons and said that the events of the day were “unjustified and unjustifiable.”
1640s, from un- (1) "not" + justifiable. Related: Unjustifiably.
1520s, from Old French justifiable, from justifiier (see justify). Earlier in same sense was justificable (mid-15c.). Related: Justifiably (mid-15c.).