nullum crimen, nulla poena sine praevia lege poenali

no crime, no punishment without a previous penal law

Notes

Legal principle meaning that one cannot be penalised for doing something that is not prohibited by law. It also means that penal law cannot be enacted retroactively.

Words

sino – allow, leave undone, let, permit, suffer, to allow
crimen – an accusation, cause of a crime, charge, crim, fault, guilt
lego – appoint, choose, collect, pass through, read, select, to gather
poena – pain, penalty, punishment