fluorine

noun

Etymology: From Latin fluor (“flow”) + -ine. Coined by British chemist Humphry Davy in 1813.

1. The chemical element (symbol F) with an atomic number of 9. It is the lightest of the halogens, a pale yellow-green, highly reactive gas that attacks all metals.
2. An atom of this element.

   “an octahedron of fluorines”