fluorine

 
Pronunciation: /ˈflʊəriːn, ˈflɔː-/

noun

[mass noun]
  • the chemical element of atomic number 9, a poisonous pale yellow gas of the halogen series. It is the most reactive of all the elements, causing very severe burns on contact with skin. (Symbol: F)

Origin:

early 19th century: from fluor (see fluorspar) + -ine4