from The American Heritage® Dictionary of the English Language, 5th Edition.
- noun A radioactive isotope of radon, Rn-219, having a half-life of 3.96 seconds and produced by the disintegration of actinium.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun Any of the
radioactive isotopesof radon
- noun Any radioactive isotope of an
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- noun any of a series of radioactive elements with atomic numbers 89 through 103
from The American Heritage® Dictionary of the English Language, 4th Edition
[actin(ium) + –on.]