hydrofluoric acid

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

• noun A colorless, fuming, corrosive, dangerously poisonous aqueous solution of hydrogen fluoride, HF, used to etch or polish glass, pickle certain metals, and clean masonry.

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

• noun chemistry A solution of hydrogen fluoride, HF, in water; it is a weak but very corrosive acid, used in the production of fluorine compounds, and in metallurgy.

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

• noun a weak poisonous liquid acid; formed by solution of hydrogen fluoride in water