from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A unit expressing the rate of decay of radioactive material, equal to one million disintegrations per second.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. An obsolete unit of radioactivity (symbol: rd), defined as the activity of a quantity of radioactive material in which one million nuclei decay per second.
After Ernest Rutherford.(American Heritage® Dictionary of the English Language, Fourth Edition)
After Ernest Rutherford. (Wiktionary)