noun. An artificially produced radioactive element with atomic number 108 that has known isotopes with mass numbers ranging from 263 to 277, all of which decay by alpha particle emission or spontaneous fission. The isotope with the longest confirmed half-life (16.5 minutes) is Hs-277. cross-reference: Periodic Table.

noun. An artificially-produced transuranic chemical element (symbol Hs) with atomic number 108.

noun. a radioactive transuranic element

"Researchers at Lawrence Berkeley National Laboratory in California saw the isotopes of rutherfordium, seaborgium, hassium, darmstadtium, and copernicium by watching the decay of the yet-to-be-named element 114, a synthetic element first produced about a decade ago."

Hessen  

hassium-270  

chemical element  element