etalon

American  

[eyt-l-on] / ˈeɪt lˌɒn /

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.

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etalon British  

/ ˈɛtəˌlɒn /

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

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Etymology

Origin of etalon

1900–05; < French; Middle French estalon standard, derivative of Old French estal place < Germanic; see stall ¹