einsteinium

 
Pronunciation: /ʌɪnˈstʌɪnɪəm/

noun

[mass noun]
  • the chemical element of atomic number 99, a radioactive metal of the actinide series. Einsteinium does not occur naturally and was discovered in 1953 in debris from the first hydrogen bomb explosion. (Symbol: Es)

Origin:

1950s: from the name of Albert Einstein, Albert + -ium