[floor-een, -in, flawr-, flohr-]
noun Chemistry.
the most reactive nonmetallic element, a pale-yellow, corrosive, toxic gas that occurs combined, especially in fluorite, cryolite, phosphate rock, and other minerals. Symbol: F; atomic weight: 18.9984; atomic number: 9.

1805–15; fluor(ic) + -ine1

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World English Dictionary
fluorine or fluorin (ˈflʊəriːn, ˈflʊərɪn)
a toxic pungent pale yellow gas of the halogen group that is the most electronegative and reactive of all the elements, occurring principally in fluorspar and cryolite: used in the production of uranium, fluorocarbons, and other chemicals. Symbol: F; atomic no: 9; atomic wt: 18.9984032; valency: 1; density: 1.696 kg/m³; relative density: 1.108; freezing pt: --219.62°C; boiling pt: --188.13°C
fluorin or fluorin

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Word Origin & History

1813, non-metallic element, coined by Eng. chemist Sir Humphry Davy (1778-1829) from fluorspar ("calcium fluoride," modern fluorite), the name of the mineral where it was first found, from L. fluor, originally meaning "a flowing, flow" (see fluent). The mineral name was given
by Georg Agricola in 1546, translating Ger. name flusse, so called because it melts easily.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

fluorine fluor·ine (flur'ēn', -ĭn, flôr'-)
Symbol F
A highly corrosive poisonous gaseous halogen element, the most reactive of all the elements. Atomic number 9; atomic weight 18.9984; melting point -219.62°C; boiling point -188.14°C (at 1 atmosphere); specific gravity of liquid 1.108 (at boiling point); valence 1.

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American Heritage
Science Dictionary
fluorine   (flr'ēn')  Pronunciation Key 
Symbol F
A pale-yellow, poisonous, gaseous element of the halogen group. It is highly corrosive and is used to separate certain isotopes of uranium and to make refrigerants and high-temperature plastics. It is also added in fluoride form to the water supply to prevent tooth decay. Atomic number 9; atomic weight 18.9984; melting point -223°C; boiling point -188.14°C; specific gravity of liquid 1.108 (at boiling point); valence 1. See Periodic Table.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
Other patches of stone have been bleached white by chlorine and fluorine gases
  pouring from the vent.
Because of their fluorine content, they're persistent.
At high pH, the fluorine groups become charged and protect the membrane from
  chlorine and clogging.
Many easily available elements such as sodium and fluorine are dangerous if
  touched, inhaled or allowed to combine with others.
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