hespériumcommon nounSyllable DecompositionhespériumEtymologyexpandfrom Latin hesperia (west, sunset) with the suffix -ium.Definition1. Chemical element that Enrico Fermi and his collaborators believed they had synthesized by bombarding uranium with neutrons, with atomic number 94 and symbol Hs (or Es, for esperium, according to sources). With the discovery of nuclear fission in 1938, it became clear that it was actually just barium and other debris (krypton, etc.).flags.désuetchimieexpandTranslationsgerman:Hesperiumenglish:esperiumitalian:esperioSee alsoespérium (cn.)