lanthanum (n.)

metallic rare earth element, 1841, coined in Modern Latin by Swedish chemist and mineralogist Carl Gustav Mosander (1797-1858), who discovered it in 1839, from Greek lanthanein "to lie hidden, escape notice," from PIE root *ladh- "to be hidden" (see latent). So called because the element was "concealed" in the earth from which he extracted it.