ADJ-GRADED
（尤指伤害他人的行为）不能证明为正当的，无可辩解的，没有道理的
If you describe an action, especially one that harms someone, as unjustifiable, you mean there is no good reason for it.
例句
Using these missiles to down civilian aircraft is simply immoral and totally unjustifiable.
用这些导弹击落民用飞机是极不道德也是完全没道理的。