Etymological origins of certain French words often hide in plain sight; all the clues are there, but we never give them a second thought. One such 'now I think of it, it's obvious' word is lunettes (French for glasses, or spectacles), un mot (word) that we all learned at school and probably use on a regular basis (especially readers that make regular visits to the optician). But perhaps without questioning its linguistic origins.
If you do know what lunettes are, chances are that you also know the words for le jour et la nuit (day and night) and even le soleil et la lune (the sun and the moon). And there's our root for spectacles, with its direct link to the moon: la lune.
Since around the year 1200, lunette (incorporating lune, from the Latin luna, and the suffix -ette, meaning 'little') referred to a moon-shaped object, and by the end of the 13th century, when the Italians were pioneering the first eyeglasses for reading, the word more specifically referred to 'polished glass or metal plate of a circular mirror'.
Today the official meaning of lunettes is thus: Instrument d'optique, généralement de forme cylindrique, comportant le plus souvent un objectif et un oculaire, servant à augmenter le diamètre apparent des objets éloignés et à en permettre une observation plus nette et plus distincte.
(An optical instrument, usually cylindrical in shape, usually with an objective and an eyepiece, used to increase the apparent diameter of distant objects and to allow a clearer and more distinct observation.)