HF

from WordNet (r) 3.0 (2006)

Hf
    n 1: a grey tetravalent metallic element that resembles
         zirconium chemically and is found in zirconium minerals;
         used in filaments for its ready emission of electrons [syn:
         {hafnium}, {Hf}, {atomic number 72}]
    2: 3 to 30 megahertz [syn: {high frequency}, {HF}]

from The Collaborative International Dictionary of English v.0.48

Hydrofluoric \Hy`dro*flu*or"ic\, a. [Hydro-, 2 + fluoric.]
   (Chem.)
   Pertaining to, or containing, hydrogen and fluorine;
   fluohydric; as, hydrofluoric acid.
   [1913 Webster]

   {Hydrofluoric acid} (Chem.), a colorless, mobile, volatile
      liquid, {HF}, very corrosive in its action, and having a
      strong, pungent, suffocating odor. It is produced by the
      action of sulphuric acid on fluorite, and is usually
      collected as a solution in water. It attacks all
      silicates, as glass or porcelain, is the agent employed in
      etching glass, and is preserved only in vessels of
      platinum, lead, caoutchouc, or gutta-percha.
      [1913 Webster]

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

HF
       Have Fun (slang, Usenet, IRC)