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. [ 1913 Webster ]