Noah Webster's Dictionary (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.

Multi-Version Concordance Unimpeachable (1 Occurrence) 1 Corinthians 1:8 who shall also confirm you to the end, unimpeachable in the day of our Lord Jesus Christ. (DBY)