From Longman Dictionary of Contemporary Englishunflaggingun‧flag‧ging /ʌnˈflæɡɪŋ/ adjective CONTINUE/NOT STOPcontinuing strongly and never becoming tired or weak his unflagging energy
Examples from the Corpus
unflagging• Her unflagging ambition more than made up for her lack of education.• In practice brute consistency breeds believability and it's unflagging consistency that convinces others of personal commitment.• The sound of his unflagging footsteps was his only company.• Dating from 1911 they not only show how he moved towards complete abstraction but also his unflagging inventiveness.• As such, he had shown unflagging support for the Axis cause. 