an instrument for measuring wavelengths of light and very small distances and thicknesses, for determining indices of refraction, and for analyzing small parts of a spectrum by means of the interference phenomena of light
See interferometer in American Heritage Dictionary 4
(ĭnˌtər-fə-rŏmˈĭ-tər)
noun
Any of several optical, acoustic, or radio frequency instruments that use interference phenomena between a reference wave and an experimental wave or between two parts of an experimental wave to determine wavelengths and wave velocities, measure very small distances and thicknesses, and calculate indices of refraction.