lanthanide series

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The set of chemically related elements with properties similar to those of lanthanum, with atomic numbers from 57 to 71; the rare-earth elements.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the rare-earth elements with atomic numbers 57 through 71; having properties similar to lanthanum