As a proper noun IUPAC
is acronym of International Union of Pure and Applied Chemistry|lang=en: an organization that establishes official names of chemical elements and compounds.
As a noun lanthanoid is
lanthanide.
iupac
Proper noun
(
en proper noun)
(chemistry) : an organization that establishes official names of chemical elements and compounds.
lanthanoid
English
Noun
(
en noun)
(inorganic chemistry) lanthanide
Usage notes
*This is the IUPAC preferred terminology.