cāsū adv. abl. of casus, by chance, casually, by accident, accidentally: casu Romae esse: id evenit non temere nec casu: sive casu sive consilio deorum, Cs.: accidit casu ut, etc., N.: casu te sortiri amicum, H.: si Pallerem casu, H.: casu tenebant bracchia nati, O.