early 15c., "plug, bung," from a nasalized variant of Old French tapon "piece of cloth to stop a hole" (14c.), a suffixed form of Frankish *tappo "stopper, plug," related to Old High German zapfo and Old English tæppa "stopper" (see tap (n.1)). Meaning "wooden plug for the muzzle of a gun" (to keep out rain or seawater) is recorded from 1620s.
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.