un·im·peach·able /ˌʌnɪmˈpiʧəbəl/
  (a.)無懈可擊的,無可指責的,無過失的
  Un·im·peach·a·ble a. Not impeachable; not to be called in question; exempt from liability to accusation; free from stain, guilt, or fault; irreproachable; blameless; as, an unimpeachable reputation; unimpeachable testimony. --Burke. -- Un*im*peach*a*ble*ness, n. -- Un*im*peach*a*bly, adv.
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  unimpeachable
       adj 1: beyond doubt or reproach; "an unimpeachable source"
       2: free of guilt; not subject to blame; "has lived a blameless
          life"; "of irreproachable character"; "an unimpeachable
          reputation" [syn: blameless, inculpable, irreproachable]
       3: completely acceptable; not open to exception or reproach;
          "two unexceptionable witnesses"; "a judge's ethics should
          be unexceptionable" [syn: unexceptionable]