noun
: a colorless mobile fuming corrosive poisonous liquid or gas HF or (HF) n that yields hydrofluoric acid when dissolved in water, is made usually by the action of sulfuric acid on fluorite, and is used chiefly in the manufacture of fluorine and fluorides and as a catalyst especially in the alkylation of branched-chain paraffins with olefins to produce superior motor fuels — called also anhydrous hydrofluoric acid