Lewis & Short

irrĕlĭgĭōsĭtas (inr-), ātis, f. [irreligiosus], irreligion, impiety (eccl. Lat.), Tert. Apol. 24; Salv. Gub. Dei, 6, 15: inexpiabilis, Hilar. in Matt. 5, 13; id. Trin. 1, 36 al.