lanthanum

American  

[lan-thuh-nuhm] / ˈlæn θə nəm /

noun

Chemistry.

1. a rare-earth, trivalent, metallic element, allied to aluminum, found in certain minerals, as monazite. La; 138.91; 57; 6.15 at 20°C.

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lanthanum British  

/ ˈlænθənəm /

noun

1. 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

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lanthanum Scientific  

/ lăn′thə-nəm /

1. 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.

2. See Periodic Table

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Etymology

Origin of lanthanum

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

Example Sentences

Europium is crucial for television screens, cerium is used for polishing glass and refining oil, lanthanum makes a car's catalytic converters operate -- the list of uses in today's economy is virtually endless.

From Barron's • Oct. 16, 2025

"The objective of the liquid separation unit will be to purify cerium on one side, lanthanum on the other side," explains production manager Florian Gouneau as we walk up a flight of metal stairs.

From BBC • Aug. 6, 2025

But, at room temperature, the number of hydrogens attached to lanthanum fluctuates between 2 and 3, making it impossible to have efficient conduction.

From Science Daily • Dec. 22, 2023

Loeb says traces of three rare elements — beryllium, lanthanum and uranium — suggest the spheres come from outside of our solar system.

From Salon • Sep. 1, 2023

Didym�ium, a rare metallic element, occurring along with lanthanum in the mineral cerite as discovered by Mosander in 1842.

From The New Gresham Encyclopedia Volume 4, Part 1: Deposition to Eberswalde by Various