lanthanum

[lan-thuh-nuhm]
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.

Origin:
< Neo-Latin (1841), equivalent to lanthan- (< Greek lanthánein to escape notice; referring to its position on the periodic table) + -um, variant of -ium -ium

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World English Dictionary
lanthanum (ˈlænθənəm)
 
n
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
 
[C19: New Latin, from Greek lanthanein to lie unseen]

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Word Origin & History

lanthanum
"metallic rare earth element," 1841, coined by Swedish chemist and mineralogist Carl Gustav Mosander (1797-1858), who discovered it in 1839, from Gk. lanthanein "to lie hidden, escape notice," because the element was "concealed" in rare minerals.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

lanthanum lan·tha·num (lān'thə-nəm)
n.
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.

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Science Dictionary
lanthanum   (lān'thə-nəm)  Pronunciation Key 
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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Encyclopedia Britannica
Encyclopedia

lanthanum

((La), chemical element, rare-earth metal of transition Group IIIb of the periodic table, prototype of the lanthanoid series of elements. Lanthanum is a ductile and malleable, silvery-white metal, soft enough to be cut with a knife. The element was discovered as the oxide (lanthana) in 1839 by Carl Gustaf Mosander, who distinguished it from cerium oxide (ceria). Its name is derived from the Greek lanthanein, meaning "to be concealed," indicating that it is difficult to isolate

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Lanthanum binds with phosphorus to form insoluble lanthanum phosphate.
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