lithium

Etymology

From New Latin lithium, from Ancient Greek λίθος (líthos, “stone”) + -ium.

noun

1. (uncountable) The simplest alkali metal, the lightest solid element, and the third lightest chemical element (symbol Li) with an atomic number of 3. It is a soft, silvery metal.
   Already, beautiful places are being wrecked by an electric vehicle resource rush. Lithium mining, for example, is now poisoning rivers and depleting groundwater from Tibet to Bolivia. 2019, George Monbiot, “Cars are killing us. Within 10 years, we must phase them out”, in Guardian.
2. (countable) A single atom of this element.
3. (pharmacology, uncountable) Lithium carbonate or other preparations of lithium metal used as a mood stabiliser to treat manic depression and bipolar disorders.
   There's more: Part of the reason I am so meek is that I stopped taking my lithium a few weeks before. It's not that I have a death wish, and it's not that I'm like Axl Rose and think that lithium makes me less manly (he supposedly stopped taking it after his first wife told him that his dick wasn't as hard as it used to be and that sex with him was lousy;[…]). 1994, Elizabeth Wurtzel, Prozac Nation: Young and Depressed in America, Houghton Mifflin, page 4
   Lithium has been used as a mood stabiliser for 50 years but its action mechanism is still unclear. 2008, Barbara Kozier, Fundamentals of Nursing: Concepts, Process and Practice, Pearson Education, page 191
4. A lithium battery.