Synonyms for HF (same or very similar meaning)
WordNet sense 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):
hafniumWordNet sense 2 (3 to 30 megahertz):
high frequencyFrom the ODE community, based on WordNetadd/edit