hydrogen fluoride

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A colorless, fuming corrosive liquid or a highly soluble corrosive gas, HF, 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.

Wiktionary

1. n. 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

WordNet 3.0

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