OBDURATE is validvalid

stubborn [adj] : OBDURATELY [adv], OBDURATENESS [n]

75,201 of 196,601 in NWL2023·also valid in CSW24

stubbornly persistent in wrongdoing [adj OBDURATELY] / to make obdurate, harden physically [v OBDURATED, OBDURATING, OBDURATES]