- Obiter Dicta – Things which are said in passing. Remarks of a judge which are not necessary to reaching a decision, but are made as comments, illustrations or thoughts.
- Omne sacramentum debet esse de certa scientia – Every oath ought to be of certain knowledge.
- Omnia delicta in aperto leviora sunt – All crimes (committed) in the open are (considered) lighter.
- Omnia praesumuntur contra spoliatorem – All things are presumed against a wrongdoer.
- Onus Probandi – Burden of proof.
- Optima legum interpres est consuetudo – The best interpreter of laws is custom.
- Optimus interpres rerum est usus – The best interpreter of things is usage.
- Overrule – Reject or disallow by exercising one’s superior authority.
