- elf, hob, gremlin, pixie, pixy, brownie, imp - (folklore) fairies that are somewhat mischievous
--1 is a kind of fairy, faery, faerie, sprite
--1 has particulars: leprechaun; sandman - extremely low frequency, ELF - below 3 kilohertz
--2 is a kind of radio frequency
--2 is a part of electromagnetic spectrum