[ pruh-mee-thee-uh m ]
/ prəˈmi θi əm /

noun Chemistry.

a rare-earth, metallic, trivalent element. Symbol: Pm; atomic number: 61.

Nearby words

  1. promethea moth,
  2. promethean,
  3. prometheus,
  4. prometheus bound,
  5. prometheus unbound,
  6. promilitary,
  7. prominence,
  8. prominences,
  9. prominent,
  10. prominent heel

Origin of promethium

From New Latin, dating back to 1945–50; see origin at Prometheus, -ium Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for promethium


/ (prəˈmiːθɪəm) /


a radioactive element of the lanthanide series artificially produced by the fission of uranium. Symbol: Pm; atomic no: 61; half-life of most stable isotope, 145 Pm: 17.7 years; valency: 3; melting pt: 1042°C; boiling pt: 2460°C (approx.)

Word Origin for promethium

C20: New Latin from Prometheus

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

Word Origin and History for promethium



radioactive element, long one of the "missing elements," 1948, so called by discoverers Jacob Marinsky and Lawrence Glendenin, who detected it in 1945 in the fusion products of uranium while working on the Manhattan Project. From Prometheus, who stole fire from the gods and was punished for it, + element name ending -ium. "The name not only symbolizes the dramatic way in which the element may be produced in quantity as a result of man's harnessing of the energy of nuclear fission, but also warns man of the impending danger of punishment by the vulture of war." [Marinsky and Glendenin]

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for promethium


[ prə-mēthē-əm ]

n. Symbol Pm

A radioactive rare-earth element prepared by fission of uranium. Pm 145 is the longest-lived isotope with a half-life of 17.7 years. Atomic number 61.

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

Science definitions for promethium


[ prə-mēthē-əm ]


A radioactive metallic element of the lanthanide series. Promethium does not occur in nature but is prepared through the fission of uranium. It has 17 isotopes, one of which is used to make long-lived miniature batteries that work at extreme temperatures for up to five years. The longest-lived isotope, Pm 147, has a half-life of 2.5 years and is used as a source of beta rays. Atomic number 61; melting point 1,168°C; boiling point 2,460°C; valence 3. See Periodic Table.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.