malum in se n., pl. mala in se [L. malum offense, wrong, evil (1); in in, on (2); se itself (3): wrong in itself.] Law. A wrong in itself. An offense such as murder which is evil, viewed either from its own nature or by natural law. The old division of crimes into mala in se … and mala prohibita … epitomises a division of society’s attitudes towards “technical breaches of the law” and those of offences touching deep-rooted moral attitudes (Curzon 1979:40). Cf. malum prohibitum.
From Word Dictionary of Foreign Expressions.