| Acronym | Meaning |
 | O | Oberst - Observer - Obstacle - Octal - Officer - Official - Oh - Operational - Operator - Oprah (magazine) - Outstanding -Oxygen |
| NC3A OR NC?A | NATO Consultation |
| TSCA | Toxic Substances Control Act (tosca) |
| DXA | Dual-energy X-ray Absorptiometry |
| CINEOS | Campo Imperatore Near-Earth Objects Survey |
| DM | Dominica (ISO 3166 Digram) -Dungeon Master (role-playing Games) |
| EPO | Esperanto Language (ISO 639-2 Code) |
| ADAT | Alesis Digital Audio Tape (recording Format) |
| COK | Cook Islands (ISO 3166 Trigram) |
| JREF | James Randi Educational Foundation |
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