lithium

 
Pronunciation: /ˈlɪθɪəm/

noun

[mass noun]
  • the chemical element of atomic number 3, a soft silver-white metal. It is the lightest of the alkali metals. (Symbol: Li)
  • lithium carbonate or another lithium salt, used as a mood-stabilizing drug.

Origin:

early 19th century: from lithia + -ium