(1):

(a.) Of or pertaining to punishment, to penalties, or to crimes and offenses; pertaining to criminal jurisprudence

(2):

(a.) Enacting or threatening punishment; as, a penal statue; the penal code.

(3):

(a.) Incurring punishment; subject to a penalty; as, a penalact of offense.

(4):

(a.) Inflicted as punishment; used as a means of punishment; as, a penal colony or settlement.