From Longman Dictionary of Contemporary Englishunimpeachableun‧im‧peach‧a‧ble /ˌʌnɪmˈpiːtʃəbəl◂/ adjective formal GOOD/EXCELLENTCERTAINLY/DEFINITELYso good or definite that criticism or doubt is impossible unimpeachable morals —unimpeachably adverb
Examples from the Corpus
unimpeachable• But it gives Tom an unimpeachable alibi.• Avoid detached signatures, unless they are of extreme rarity and unimpeachable authenticity.• Collectively its dedication, despite all difficulties, constituted an unimpeachable example.• One person has wide and reliable knowledge of cars, as well as an unimpeachable moral character.• Its author has an unimpeachable pedigree: stories in the New Yorker, degrees from Stanford and Harvard.• unimpeachable statistical proof• She possessed unimpeachable status, for she was the Firstborn.• So you devise a situation where an absolutely unimpeachable witness sees the murderer in black leaving the scene of the crime. 