ma·ser 
(māzər)
(māzər)n.
1. A device that generates or amplifies electromagnetic radiation, especially microwaves, of a coherent wavelength by stimulated emission.
2. A natural object or region of space that acts like a maser, as a star-forming region of intersellar space.
[m(icrowave) a(mplification by) s(timulated) e(mission of) r(adiation).]