| Abbreviation | Definition |
|---|---|
| OMT | Ohio Medical Transportation |
| ON | Ontario Nature |
| ONA | Outreach to New Americans |
| ONAD | Organization for Nonviolence and Development |
| ONAF | Organizzazione Nazionale Assaggiatori Formaggi |
| ONAF | Organizzazione Nazionale Assaggiatori Formaggio |
| ONAG | Organisation des Nations Autochtones de Guyane |
| ONB | Operation New Birmingham |
| ONBGFF | Old NewsBoys' GoodFellow Fund |
| ONF | Oncology Nursing Forum |
| ONF | Oncology Nursing Foundation |
| ONF | Ontario Neurotrauma Foundation |
| ONF | Oregon Nurses Foundation |
| ONG | Organisation Non Gouvernementale |
| ONGO | Overseas Non-Governmental Organization |
| ONK | Old North Knoxville |
| ONN | Online Noetic Network |
| ONS | Oncology Nursing Society |
| ONSF | Oncology Nursing Society Foundation |
| ONSFCLIR | Oncology Nursing Society Foundation Center for Leadership, Information, and Research |