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- Registered Dental Assistant
- Recommended Daily Allowance, older standard replaced by Recommended Dietary Allowance (below)
- Recommended Dietary Allowance, dietary guidelines for nutrient intake
- Rassemblement Démocratique Africain (African Democratic Rally), a political party found formed in 1946 in French West Africa
- Regional Development Agency, a public sector organisation in England
- Rda, an Enochian name of a minor angel
- Reader's Digest Association, a US magazine-publisher
- Redland railway station, a railway station in Bristol, England with the National Rail code "RDA"
- Rules of Decision Act, a federal law in the United States
- Research and Development Array, a cosmic ray detector development project in Colorado, US
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