Any of a series of 15 naturally occurring metallic elements. The lanthanides include elements having atomic numbers 57 (lanthanum) through 71 (lutetium). They are grouped apart from the rest of the elements in the Periodic Table because they all behave in a similar way in chemical reactions.
Any of the rare-earth elements (lanthanide series)
Origin of lanthanide
- lanthan(um) –ide
From American Heritage Dictionary of the English Language, 5th Edition