Einsteinium

[ahyn-stahy-nee-uh m] /aɪnˈstaɪ ni əm/

noun, Chemistry, Physics.
1.
a transuranic element. Symbol: Es; atomic number: 99.
/aɪnˈstaɪnɪəm/
noun
1.
a metallic transuranic element artificially produced from plutonium. Symbol: Es; atomic no: 99; half-life of most stable isotope, 252Es: 276 days
n.

discovered in the debris of a 1952 U.S. nuclear test in the Pacific, named 1955 for physicist Albert Einstein (1879-1955).

einsteinium ein·stein·i·um (īn-stī’nē-əm)
n.
Symbol Es
A radioactive transuranic element synthesized by neutron irradiation of plutonium or other elements. Its longest-lived isotope is Es 254 with a half-life of 275 days. Atomic number 99; melting point 860°C.
einsteinium
(īn-stī’nē-əm)
Symbol Es
A synthetic, radioactive metallic element of the actinide series that is usually produced by bombarding plutonium or another element with neutrons. It was first isolated in a region near the explosion site of a hydrogen bomb. Its longest-lived isotope is Es 254 with a half-life of 276 days. Atomic number 99; melting point 860°C. See Periodic Table.