sox n.

"knitted or woven covering for the foot, short stocking," Middle English sok, from Old English socc "slipper, light shoe," from Latin soccus "slipper, light low-heeled shoe," probably a variant of Greek sykkhos, word for a kind of shoe, perhaps from Phrygian or another Asiatic language. Beekes pointes to a source that "supposes a loan from the Caucasus, which may also be found in Av[estan] haxa- [n.] 'sole of the foot' ...." The Latin word was borrowed generally in West Germanic (Middle Dutch socke, Dutch sok, Old High German soc, German Socke).

Also in reference to the kind of light shoe worn by ancient actors in comedy, hence, in phrases, sock as "comedy" as distinct from "tragedy" (represented by buskin). To knock the socks off (someone) "beat thoroughly" is recorded from 1845, American English colloquial. Colloquial put a sock in it "stop speaking" is by 1919. Teen slang sock hop is c. 1950, from dancing shoeless.

also bobby socks, 1943, from diminutive of bob (n.2) + sox. So called because they are "shortened" compared to knee-socks. Derivative bobby-soxer "adolescent girl," especially with reference to fans of popular crooners, is attested by 1944.

Months ago colored bobby sox folded at the top were decreed, not by anyone or any group but, as usual, by a sudden mysterious and universal acceptance of the new idea. Now no teen-ager dares wear anything but pure white socks without a fold. [Life magazine, Dec. 11, 1944]