ununoctium

Systematic element name, from un- +‎ un- +‎ oct- +‎ -ium.

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ununoctium (uncountable)

1. (dated) The systematic element name for the chemical element with atomic number 118 (symbol Uuo); now named oganesson.
   • 2015 December 30, “Discovery and Assignment of Elements with Atomic Numbers 113, 115, 117 and 118”, in IUPAC‎^[1]:

     “The chemistry community is eager to see its most cherished table finally being completed down to the seventh row. IUPAC has now initiated the process of formalizing names and symbols for these elements temporarily named as ununtrium, (Uut or element 113), ununpentium (Uup, element 115), ununseptium (Uus, element 117), and ununoctium (Uuo, element 118)” said Professor Jan Reedijk, President of the Inorganic Chemistry Division of IUPAC.

   • 2016 March 1, Willem H. Koppenol, John Corish, Javier García-Martínez, Juris Meija and Jan Reedijk, “How to name new chemical elements (IUPAC Recommendations 2016)”, in Pure and Applied Chemistry‎^[2], volume 88, number 4, →DOI, archived from the original on 11 November 2025, page 404:

     Prior to and during the naming process, the element may be referred to by its atomic number, for example as in ‘element 118’, or by its provisional systematic name, ‘ununoctium’.

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ununoctium

1. oganesson

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ununoctium n (uncountable, no diminutive)

1. ununoctium

Derived from ūn(us) (“one”) + ūn(us) + oct(ō) (“eight”) +‎ -ium (chemical element suffix), in reference to the element's atomic number (118).

• (Classical Latin) IPA^(key): [uː.nuːˈnɔk.ti.ũː]
• (modern Italianate Ecclesiastical) IPA^(key): [u.nuˈnɔk.t͡si.um]

ūnūnoctium n (genitive ūnūnoctiī); second declension

1. (New Latin) ununoctium

Second-declension noun (neuter).

• Italian: ununoctio

ununoctium n (genitive singular ununoctia, declension pattern of mesto)

1. ununoctium (element)