maser

Short definition from Wiktionary

Noun

1. 1
   a device for the coherent amplification or generation of electromagnetic radiation (especially of microwave frequency) by the use of excitation energy in resonant atomic or molecular systems
2. 2
   Any celestial object that generates microwaves using the same method
3. 3
   Obsolete spelling of mazer.
4. 4
   Acronym of microwave amplification by the stimulated emission of radiation.