Ununennium (Uue) is a synthetic chemical element with the atomic number 119, which is the element with the highest known atomic number (and therefore the highest atomic mass, at 294). This element does not occur naturally, and is formed by the collision of massive atomic nuclei to create a slightly lighter nucleus which then decays to ununennium. It was first created by the Flerov Laboratory of Nuclear Reactions in Dubna, Russia on February 11th 2004, and was initially suggested to be called "ununennium", though this remains an unofficial and non-systematic name.

Although ununennium has been confirmed by the Joint Working Party of the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) as being an authentic chemical element, it has yet to be formally named.