- Octavia, Empress, consort of Nero, Emperor of Rome, approximately 42-621
- Oedipus (Greek mythological figure)1
- On style (Demetrius)1
- Orden de Santiago1
- Orso, Saint1
- Orthodox Eastern Church1
- Painted bindings1
- Paltonibus, Antonio de1
- Pannilini, Francesco1
- Pannilini, Guglielmo1
- Parent and child (Law)1
- Paul V, Pope, 1552-16211
- Pentecost1
- Petronibus, Agabitus de1
- Petronibus, Ludovicus Salimbeni de1
- Petronibus, Petronius Caterini de1
- Petronibus, Petronius de1
- Phaedra (Greek mythological character)1
- Piccolomini d'Aragona, Antonio di Nanni Todeschini, Duke of Amalfi1
- Piccolomini di Castiglia e d'Aragona, Giacomo di Nanni Todeschini1