lanthanide

noun

Any rare earth element of the lanthanide series (atomic numbers 57 through 71).

Any of the 14 rare earth elements from cerium (or from lanthanum) to lutetium in the periodic table; because their outermost orbitals are empty, they have very similar chemistry; below them are the actinides.

Any element of the lanthanide series (atomic numbers 57 through 71).