disk (n.) Look up disk at Dictionary.com
American English preferred spelling, 1660s, "round flat surface," from Latin discus "quoit, discus, disk," from Greek diskos "disk, quoit, platter," related to dikein "to throw," from PIE *dik-skos-, possibly from root *deik- "to show, pronounce solemnly; also in derivatives referring to the directing of words or objects" [Watkins]. The notion is "to throw" as "to direct an object."

Sense of "phonograph disk" is 1888; computing sense is from 1947. Disk jockey first recorded 1941; dee-jay is from 1955; DJ is 1961; video version veejay is 1982. Disk-drive is from 1952.