1. A soft, silvery, highly reactive metallic element that is used as a heat transfer medium, in thermonuclear weapons, and in various alloys, ceramics, and optical forms of glass. Atomic number 3; atomic weight 6.941; melting point 179°C; boiling point 1,317°C; specific gravity 0.534; valence 1.
2. Any of several salts of lithium, especially lithium carbonate.

[From LITHIA.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.