Home › Words › U › ununseptiumununseptium/uːnuːnˈsɛpti.əm/ununseptium · noun — the systematic element name for the chemical element with atomic number 117 (symbol Uus). The element is now named tennessine.Definition from Wiktionary (CC BY-SA 3.0).ununseptium is pronounced /uːnuːnˈsɛpti.əm/.EtymologySystematic element name, from un- + un- + sept- + -ium.nounThe systematic element name for the chemical element with atomic number 117 (symbol Uus). The element is now named tennessine.Definitions & examples from Wiktionary (CC BY-SA 3.0).