from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A naturally radioactive, silvery, metallic transuranic element, occurring in uranium ores and produced artificially by neutron bombardment of uranium. Its longest-lived isotope is Pu 244 with a half-life of 76 million years. It is a radiological poison, specifically absorbed by bone marrow, and is used, especially the highly fissionable isotope Pu 239, as a reactor fuel and in nuclear weapons. Atomic number 94; melting point 640°C; boiling point 3,235°C; specific gravity 19.84; valence 3, 4, 5, 6. See Table at element.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The transuranic chemical element with atomic number 94 and symbol Pu.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a solid silvery grey radioactive transuranic element whose atoms can be split when bombarded with neutrons; found in minute quantities in uranium ores but is usually synthesized in nuclear reactors; 13 isotopes are known with the most important being plutonium 239
After the dwarf planet Pluto (from the fact that it follows neptunium in the periodic table).(American Heritage® Dictionary of the English Language, Fourth Edition)
After Pluto (the entity formerly considered to be a planet). (Wiktionary)