unimpeachable āļāļ·āļāļāļ°āđāļĢ unimpeachable āļāļ·āļāļāļ°āđāļĢ Difficult or impossible to impeach: an unimpeachable witness. Beyond reproach; blameless: unimpeachable behavior. Beyond doubt; unquestionable: "works of such unimpeachable greatnessâ ( Musical Heritage Review).