[ am-uh-rish-ee-uh m ]
/ ˌæm əˈrɪʃ i əm /

noun Chemistry.

a transuranic element, one of the products of high-energy helium bombardment of uranium and plutonium. Symbol: Am; atomic number: 95.

Nearby words

  1. americanize,
  2. americanized,
  3. americano,
  4. americanologist,
  5. americas,
  6. americus,
  7. amerigo vespucci,
  8. amerind,
  9. amerindian,
  10. ameristic

Origin of americium

An Americanism dating back to 1945–50; Americ(a) + -ium Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for americium


/ (ˌæməˈrɪsɪəm) /


a white metallic transuranic element artificially produced from plutonium. It is used as an alpha-particle source. Symbol: Am; atomic no: 95; half-life of most stable isotope, 243 Am: 7.4 × 10³ years; valency: 2,3,4,5, or 6; relative density: 13.67; melting pt: 1176°C; boiling pt: 2607°C (est)

Word Origin for americium

C20: from America (because it was discovered at Berkeley, California) + -ium

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medicine definitions for americium


[ ăm′ə-rĭshē-əm ]

n. Symbol Am

A white metallic synthetic element of the actinide series whose longest-lived isotopes, Am 241 and Am 243, are used as radiation sources for bone mineral analysis and in treating cancer. Atomic number 95.

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for americium


[ ăm′ə-rĭshē-əm ]

Symbol Am A synthetic, silvery-white, radioactive metallic element of the actinide series that is produced artificially by bombarding plutonium with neutrons. Americium is used as a source of alpha particles for smoke detectors and gamma rays for industrial gauges. Its most stable isotope has a half-life of 7,950 years. Atomic number 95; specific gravity 11.7; valence 3, 4, 5, 6. See Periodic Table.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.