Source : Webster's Revised Unabridged Dictionary (1913)

Fluorine \Flu"or*ine\ (? or ?; 104), n. [NL. fluorina: cf. G.
   fluorin, F. fluorine. So called from its occurrence in the
   mineral fluorite.] (Chem.)
   A non-metallic, gaseous element, strongly acid or negative,
   or associated with chlorine, bromine, and iodine, in the
   halogen group of which it is the first member. It always
   occurs combined, is very active chemically, and possesses
   such an avidity for most elements, and silicon especially,
   that it can neither be prepared nor kept in glass vessels. If
   set free it immediately attacks the containing material, so
   that it was not isolated until 1886. It is a pungent,
   corrosive, colorless gas. Symbol F. Atomic weight 19.

   Note: Fluorine unites with hydrogen to form hydrofluoric
         acid, which is the agent employed in etching glass. It
         occurs naturally, principally combined as calcium
         fluoride in fluorite, and as a double fluoride of
         aluminium and sodium in cryolite.

Source : WordNet®

fluorine
     n : a nonmetallic univalent element belonging to the halogens;
         usually a yellow irritating toxic flammable gas; a
         powerful oxidizing agent; recovered from fluorite or
         cryolite or fluorapatite [syn: {F}, {atomic number 9}]