hydrogen fluoride

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A colorless, fuming corrosive liquid or a highly soluble corrosive gas, HF, that is extremely toxic, used in the manufacture of hydrofluoric acid, as a reagent, catalyst, and fluorinating agent, and in the refining of uranium and the preparation of many fluorine compounds.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry a colourless fuming liquid or gas, having a molecular formula of HF; it dissolves in water to form hydrofluoric acid and has many industrial uses including the production of teflon and the refining of uranium; it corrodes skin, flesh and bone, and any skin contact must be avoided

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a colorless poisonous corrosive liquid made by the action of sulphuric acid on calcium fluoride; solutions in water are hydrofluoric acid