| O&A | Odontectomy and Alveolectomy 
| Others |
| O.A. | Order of Australia
| Others |
| O/A | Old Age
| Others |
| O/A | On Account
| Others |
| O/A | On Admission
| Others |
| O/A | On Arrival
| Others |
| O/A | Open Account
| Others |
| O/A | Operating As
| Others |
| OA | Obadiah Abbe
| Others |
| OA | Oben Angef
| Others |
| OA | Object Adapter
| Others |
| OA | Object Address
| Others |
| OA | Objective Area
| Others |
| OA | Obstructive Apnoea
| Others |
| OA | Occipital Artery
| Others |
| OA | Occiput Anterior
| Others |
| OA | Ocular Albinism
| Others |
| OA | Odessa American
| Others |
| OA | odontoameloblastoma
| Others |
| OA | Oesophageal Atresia
| Others |
| OA | Offer Accepted
| Others |
| OA | Office Admin
| Others |
| OA | Office Automation
| Others |
| OA | Office of Administration
| Others |
| OA | Office of Applications
| Others |
| OA | Office of Applications (now OSTA)
| Others |
| OA | Office of Audit
| Others |
| OA | Official Announcements
| Others |
| OA | Official Answer
| Others |
| OA | Ogie Alcasid
| Others |
| OA | Oil Air
| Others |
| OA | Okay Ako
| Others |
| OA | Ole Automation
| Others |
| OA | Oleic Acid
| Others |
| OA | oligoastrocytoma
| Others |
| OA | Olympic Airways
| Others |
| OA | Olympic Arms
| Others |
| OA | Omar Ahmed
| Others |
| OA | on Abbreviations
| Others |
| OA | On-board Administrator
| Others |
| OA | Onepass Aadvantage
| Others |
| OA | Online Adventures
| Others |
| OA | Online Applicant
| Others |
| OA | Open Access
| Others |
| OA | Open Agility
| Others |
| OA | Open Apple
| Others |
| OA | Open Appointment
| Others |
| OA | Open Appserver
| Others |
| OA | Open Architecture
| Others |
| OA | Operating Assembly
| Others |
| OA | Operation Administrations
| Others |
| OA | Operational Aft
| Others |
| OA | Operational Aft (DSC or MOM)
| Others |
| OA | Operational Architecture
| Others |
| OA | Operational Area
| Others |
| OA | Operational Assessment
| Others |
| OA | Operational instrumentation MDM (Manipulator Deployment Mechanism) -Aft
| Others |
| OA | Operations Aerology Shipboard METOC Division
| Others |
| OA | Operations Agreement
| Others |
| OA | Operations and Algebraic
| Others |
| OA | Operations Assistant
| Others |
| OA | Operator Algebras
| Others |
| OA | Ophthalmic Artery
| Others |
| OA | Opperate Annihilate
| Others |
| OA | Opposites Attract
| Others |
| OA | Optical Amplifier
| Others |
| OA | Optical Axis
| Others |
| OA | Option Appraisal
| Others |
| OA | Orange Arsenal
| Others |
| OA | Orbital Assembly
| Others |
| OA | Ordem dos Advogados
| Others |
| OA | Order Administration
| Others |
| OA | Order of Advocates
| Others |
| OA | Order of Alequi
| Others |
| OA | Order of the Arrow
| Others |
| OA | Ordered Application
| Others |
| OA | Org.Apache
| Others |
| OA | Organic Acid
| Others |
| OA | Organic Aerosol
| Others |
| OA | Organic Anion
| Others |
| OA | Oriental Adventures
| Others |
| OA | Original Angel
| Others |
| OA | Original Arranged
| Others |
| OA | Original Artist
| Others |
| OA | Orotic Acid
| Others |
| OA | Orthogonal Array
| Others |
| OA | Osteo-arthritis
| Others |
| OA | Other Adjustment
| Others |
| OA | Other Approval
| Others |
| OA | Other Auctions
| Others |
| OA | Outdoor Adventure
| Others |
| OA | Output Axis
| Others |
| OA | Outreach and Admissions
| Others |
| OA | Ovarian Artery
| Others |
| OA | Over Acting
| Others |
| OA | Over Actor
| Others |
| OA | Over Aged
| Others |
| OA | Overall
| Others |
| OA | Overall Accuracy
| Others |
| OA | Overall Assessment
| Others |
| OA | Overeaters And
| Others |
| OA | Overeaters Anonymous
| Others |
| OA | Overs Average
| Others |
| OA | Overzealous Academy
| Others |
| OA | Owner Agent
| Others |
| OA | Oxalic Acid
| Others |
| OA | Oxygen Activation
| Others |