a. [ Cf. F. pénitentiel. ] Of or pertaining to penitence, or to penance; expressing penitence; of the nature of penance; as, the penitential book; penitential tears. “Penitential stripes.” Cowper. [ 1913 Webster ]

Guilt that all the penitential fires of hereafter can not cleanse. Sir W. Scott. [ 1913 Webster ]

n. (R. C. Ch.) A book formerly used by priests hearing confessions, containing rules for the imposition of penances; -- called also penitential book. [ 1913 Webster ]

adv. In a penitential manner. [ 1913 Webster ]