フッ素

Etymology
Compound of. First used by Morisaburō Ichikawa in Rika Nikki (1872). was chosen for the initial fu, used by in Seimi Kaisō (1837-1847) as  from  (not used today), and by Heijirō Takehara in Kagaku Nyūmon (1867-1870) as  from. Other sources say it is from  but the Dutch translations predate English ones.

Noun

 * 1) fluorine, F
 * 2) fluorine gas
 * 3)  fluoride to prevent cavities such as sodium fluoride.

Usage notes
Commonly written with katakana instead of kanji for the portion, due to the rarity of the  character.