a. 不能防卫的, 无辩护余地的

Indefensible \In`de*fen"si*ble\, [Pref. in- not + defensible:
cf. OF. indefensible, indefensable.]
Not defensible; not capable of being defended, maintained,
vindicated, or justified; unjustifiable; untenable; as, an
indefensible fortress, position, cause, statement, etc.

Men find that something can be said in favor of what,
on the very proposal, they thought utterly
indefensible. --Burke.