Of, pertaining to, proceeding from, or expressing penitence or contrition of heart: as, penitential sorrow; penitential psalms.Eccles., pertaining to the administration of the sacrament of penance; hence, of the nature of penance or punishment.n. In the Rom. Cath. and the Gr. Ch., a book or code of canons relating to penance and the reconciliation of penitents.n. One who has undergone penitential discipline.