c. 1300, "the light, elastic outer bark of a species of oak tree native to Iberia and North Africa, used for many purposes," from Spanish alcorque "cork sole," probably from earlier Spanish corcho, from Latin quercus "oak" (see Quercus) or cortex (genitive corticis) "bark" (see corium).
In reference to the tree itself, mid-15c. From late 14c. as "cork-soled shoe." As "cork float for a fishing line," mid-15c. Meaning "cylindrical cork stopper or bung for a bottle, etc.," 1520s. As an adjective, "made of cork," 1716.