- hafnium, Hf, atomic number 72 - a gray tetravalent metallic element that resembles zirconium chemically and is found in zirconium minerals; used in filaments for its ready emission of electrons
--1 is a kind of metallic element, metal
- high frequency, HF - 3 to 30 megahertz
--2 is a kind of radio frequency
--2 is a part of electromagnetic spectrum