Unimpeachable/ˌʌnɪmˈpiːtʃəbl/ Definition 1 of 3Pro Tip 1/3Trustworthy Source Used to describe people with a proven track record of honesty and dependability. His unimpeachable nature made him the favorite employee. Pro Tip 2/3Beyond Doubt Highlights absolute trust without a need for further evidence or questioning. The unimpeachable findings solidified the research's impact. Pro Tip 3/3Positive Connotation Conveys a highly positive impression of someone's morals or behavior. She was admired for her unimpeachable honesty in all matters.