1650s, from French capsule "a membranous sac" (16c.), from Latin capsula "small box or chest," diminutive of capsa "box, case, chest" (see case (n.2)). Medicinal sense is 1875; shortened form cap is from 1942. Sense in space capsule is first recorded 1954. As an adjective from 1938. Related: Capsular.
capsule cap·sule (kāp'səl, -sōōl)
n.
A fibrous, membranous, or fatty sheath that encloses an organ or part, such as the sac surrounding the kidney or the fibrous tissues that surround a joint.
A small soluble container, usually made of gelatin, that encloses a dose of an oral medicine or a vitamin.
The thin-walled, spore-containing structure of mosses and related plants.