etalon

etalon [eyt-l-on] Word Origin noun Optics.

1. an interferometer consisting of two glass plates that reflect approximately half of each ray of light incident upon them and that are separated by a small, fixed distance: used to compare wavelengths and to study atomic spectra.

Origin of etalon 1900–05; French; Middle French estalon standard, derivative of Old French estal place Germanic; see stall1 British Dictionary definitions for etalon etalon noun

1. physics a device used in spectroscopy to measure wavelengths by interference effects produced by multiple reflections between parallel half-silvered glass or quartz plates

Word Origin for etalon C20: French étalon a fixed standard of weights and measures, from Old French estalon; see also stallion