magnum opus (L.) A great work.
mal à propos (Fr.). Ill timed.
mal de mer (Fr.). Sea-sickness.
mal de tête (Fr.). Headache.
mauvaise honte (Fr.). False modesty.
mauvais goût (Fr.). Bad taste.
medio tutissimus ibis (L.). In a medium course you will be safest.
mega biblion, mega kakon (Gr.). A great book is a great evil.
me judice (L.). I being judge; in my opinion.
memento mori (L.). Remember death.