Lewis & Short

poenālis, e, adj. [poena], of or belonging to punishment, penal (post-Aug.; esp. freq. in the jurists): opera, Plin. 18, 11, 29, § 112: poenalis aquae dirisque genitae, in the infernal regions, id. 4, 8, 15, § 31: ex lege poenali aquā et igne interdici, by the penal law, Gai. Inst. 1, § 128: actio, Dig. 40, 12, 21: causa, ib. 46, 3, 7: conditio, ib. 22, 2, 5: stipulatio, ib. 19, 2, 54 et saep.
Absol.: poenāles, ĭum, m., men subject to punishment, criminals: carcer poenalium, Cod. Just. 10, 19, 2.
Sup.: inter haec horrenda et poenalissima, exceedingly punishable or criminal, Salv. Avar. 2, 10.
Adv.: poenālĭter, by punishment or penalty (post-class.): reus poenaliter interibat, Amm. 16, 8, 2.