1. graded adjective & adjective If you say that a statement, action, or idea is indefensible, you mean that it cannot be justified or supported because it is completely wrong or unacceptable. ⇒ His action was indefensible. ⇒ She described the new policy as 'morally indefensible'.
The indefensible is something which is indefensible. ⇒ To argue otherwise is trying to defend the indefensible.
2. adjective Places or buildings that are indefensible cannot be defended if they are attacked. ⇒ The checkpoint was abandoned as militarily indefensible.
COBUILD Advanced English Dictionary. Copyright © Harper Collins Publishers