lanthanide; lanthanoid
Chemical term for the series of 15 metallic elements from lanthanum to lutetium. Both 'lanthanide' and 'lanthanoid' are used in English; 'lanthanoid' is the IUPAC-preferred term.
The lanthanoids are a group of elements belonging to Group 3 of the periodic table.
The lanthanoid contraction is a phenomenon where atomic radii become smaller than expected.