doublet

Etymology 1

From Middle English doublet, a borrowing from Old French doublet, from double, duble, doble + -et.

noun

1. A pair of two similar or equal things; couple.
2. (linguistics) One of two or more different words in a language derived from the same etymological root but having different phonological forms (e.g., toucher and toquer in French or shade and shadow in English).
3. (literature) In textual criticism, two different narrative accounts of the same actual event.
4. (lapidary) An imitation gem made of two pieces of glass or crystal with a layer of color between them.
5. (printing, US) A word or phrase set a second time by mistake.
6. (quantum mechanics) A quantum state of a system with a spin of ½, such that there are two allowed values of the spin component, −½ and +½.
7. (computing) A word (or rather, a halfword) consisting of two bytes.
8. (botany) A very small flowering plant, Dimeresia howellii.
9. A word ladder puzzle.
10. An arrangement of two lenses for a microscope, designed to correct spherical aberration and chromatic dispersion, thus rendering the image of an object more clear and distinct.
    The doublet generally used is that invented by Dr. Wollaston, and consists of two plano-convex lenses placed with their convex sides towards the eye […] 1855, Hermann Schacht, Frederick Currey, The Microscope
11. Either of two dice, each of which, when thrown, has the same number of spots on the face lying uppermost.
    to throw doublets
12. (uncountable, obsolete) A game somewhat like backgammon.
13. (radio) Dipole antenna.
14. (historical) A man’s waistcoat.

Etymology 2

From Italian giubbetta, from giubba, from Arabic جبة (“to en-wrap”).

noun

1. A man’s close-fitting jacket, with or without sleeves, worn by European men from the 1400s to the 1600s.
   He was a stout old gentleman, with a weather-beaten countenance; he wore a laced doublet, broad belt and hanger, high-crowned hat and feather, red stockings, and high-heeled shoes, with roses in them. 1819, Washington Irving, The Sketch Book, Rip Van Winkle