Encyclopedias, Almanacs, Transcripts, and Maps
- O'Daniel, Victor Francis
- O'Devany, Conor, Bl.
- O'Donnell, Edmund
- O'Fihely, Maurice
- O'Gorman, Thomas
- O'Hara, Edwin Vincent
- O'Hara, John Francis
- O'Hely, Patrick, Bl.
- O'Hurley, Dermot, Bl.
- O'Leary, Henry Joseph
- O'Neill, Sara Benedicta
- O'Reilly, Bernard
- O'Reilly, Edmund
- O'Toole, George Barry
- O? Ma?i Padme Hu?
- O?ar Hatorah
- Oak, Synod of the
- Oates Plot
- Oath More Judaico or Juramentum Judaeorum
- Oaths (in the Bible)