from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A silvery, metallic, naturally radioactive element, atomic number 93, the first of the transuranium elements. Its longest-lived isotope is Np-237 with a half-life of 2.1 million years. Found in trace quantities in uranium ores, it is produced synthetically by nuclear reactions. See Table at element.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The transuranic chemical element with atomic number 93 and symbol Np.
from the GNU version of the Collaborative International Dictionary of English
- n. A radioactive metallic element of atomic number 93, produced in nuclear reactors from Plutonium or Uranium. Symbol Np; The atomic weight of the most stable isotope is 237.0482.
from The Century Dictionary and Cyclopedia
- n. In chem., a supposed new element announced by Hermann in 1877 as present in columbite and ferro-ilmenite. Its existence has not been confirmed.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a radioactive transuranic metallic element; found in trace amounts in uranium ores; a by-product of the production of plutonium
After the planet Neptune (from the fact that it follows uranium in the periodic table).(American Heritage® Dictionary of the English Language, Fourth Edition)
After Neptune (the planet). (Wiktionary)