Definitions for "Monochromator"
a device that allows one to select a certain wavelength of monochromatic light from a polychromatic light source such as a xenon or mercury lamp
a devise that uses a diffraction grating or prism to disperse light into a spectrum of its constituent wavelengths
an instrument which accepts a light source as its input and can select not quite a single wavelength, but a narrow band of wavelengths