This is one of those words that always eludes me no matter how many times I look it up, and I’m hoping that writing about it will implant it more firmly in my brain. I’m reading Samuil A. Lurie’s Изломанный аршин [‘Broken cubit-ruler,’ an insulting nineteenth-century term for a merchant] (see this post) and enjoying it immensely; after brilliantly annotating a poem Pushkin wrote in the hope of flattering the aged Prince Yusupov into being proxy father at his upcoming wedding (it did the trick), Lurie says it’s a very pleasant work, and that if it were a Petersburg building “считалось бы эталоном т. н. фоновой застройки” — it would be considered an etalon of background architecture, the kind of building you cast an approving glance at as you walk past.
“Etalon, what the hell is an etalon,” I muttered internally as I reached for my dictionary to learn once again that it is a “standard (of weights and measures).” I figured it must come from French, and sure enough my Concise Oxford French Dictionary had étalon with the definition “standard (of weights and measures).” The etymology was given simply as “OF estel,” which wasn’t satisfying, so I turned to the OED, which surprised me by having an entry (from 1972) étalon | etalon, n., though with a very different definition: “A device used to produce interfering beams of light, consisting essentially of two plane parallel reflecting plates of fixed separation and (in some kinds) adjustable orientation.” Their etymology was “< French étalon (Fabry & Pérot 1902, in Ann. de Chimie et Physique XXV. 107), lit. ‘a standard (of weights, measures, etc.)’ < Old French estalon, estelon probably of Germanic origin: see stallion n.” I didn’t find the stallion origin particularly convincing, so I turned to the fifth edition of the AHD for something more up-to-date, and found it defined as “A type of interferometer in which incoming light is repeatedly refracted and reflected between two surfaces into multiple beams that are then focused together, causing self-interference of the light,” with this etymology:
French étalon, standard (of weight or a unit of measurement), reference point, etalon (in reference to the fixed widths between the two surfaces in the first such interferometers) < Old French estalon, standard, of Germanic origin; akin to Middle Dutch stael, model, sample.
So now you know as much about etalons as I do, and maybe the next time I run into эталон I’ll think “Ah yes, not a stallion but a standard.”