Cerium \Ce"ri*um\, n. [Named by Berzelius in 1803 from the asteroid Ceres, then just discovered (1801).]

(Chem.) A rare metallic element, occurring in the minerals cerite, allanite, monazite, etc. Symbol Ce. Atomic weight 141.5. It resembles iron in color and luster, but is soft, and both malleable and ductile. It tarnishes readily in the air.

Source: Webster's Revised Unabridged Dictionary (1913)