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[lan-thuh-nuh m] /ˈlæn θə nəm/

noun, Chemistry.
a rare-earth, trivalent, metallic element, allied to aluminum, found in certain minerals, as monazite. Symbol: La; atomic weight: 138.91; atomic number: 57; specific gravity: 6.15 at 20°C.
a silvery-white ductile metallic element of the lanthanide series, occurring principally in bastnaesite and monazite: used in pyrophoric alloys, electronic devices, and in glass manufacture. Symbol: La; atomic no: 57; atomic wt: 138.9055; valency: 3; relative density: 6.145; melting pt: 918°C; boiling pt: 3464°C

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 rare minerals.

lanthanum lan·tha·num (lān’thə-nəm)
Symbol La
A soft malleable metallic rare-earth element used in glass manufacture. Atomic number 57; atomic weight 138.91; melting point 920°C; boiling point 3,455°C; specific gravity 6.145 (at 25°C); valence 3.
Symbol La
A soft, malleable, silvery-white metallic element of the lanthanide series. It is used to make glass for lenses and lights for movie and television studios. Atomic number 57; atomic weight 138.91; melting point 920°C; boiling point 3,469°C; specific gravity 5.98 to 6.186; valence 3. See Periodic Table.


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