Definition of "oganesson"
The chemical element (Symbol Og) with atomic number 118. It is the heaviest known element. Highly radioactive, it does not occur naturally. Originally expected to be a noble gas, it is now predicted to be a reactive metallic solid, and a semiconductor or a post-transition metal.
Quotations
In January 2016 the International Union of Pure and Applied Chemistry (IUPAC) announced the discovery of four new elements, so completing the seventh row of the periodic table. They have since been named as nihonium, Nh, muscovium[sic], Mc, tennessine, Ts, and organesson[sic], Og. The procedures for naming new elements are clearly laid out by IUPAC.
2018, Mark Weller, Tina Overton, Fraser Armstrong, Jonathan Rourke, chapter 1, in Inorganic Chemistry, Oxford University Press, page 21