post-box (n.)

[mail system] c. 1500, "riders and horses posted at intervals," to provide direct and rapid communication of messages and letters from one place to another by relays, from post (n.2) on notion of riders and horses "posted" at intervals along a route. Probably formed on model of French poste in this sense (late 15c.).

The meaning "system for the conveyance of letters" is from 1660s; it is attested from 1590s in the sense of "vehicle used to convey mails;" 1670s as "a dispatch of letters from or to a place." As a newspaper name from 1680s.

"rectangular wooden container," usually with a lid, Old English box, also the name of a type of shrub, from Late Latin buxis, from Greek pyxis "boxwood," pyxion "writing table, box," made of boxwood, from pyxos "box tree," which is of uncertain origin. Beekes suggests a loan-word from Italy, as that is where the tree is native. Dutch bus, German Büchse "box; barrel of a gun," also are Latin loan-words.

Meaning "compartment at a theater" is from c. 1600 (box seat in the theatrical sense is by 1850). Meaning "pigeon-hole at a post office" is from 1832. Meaning "television" is from 1950 (earlier "gramophone player," 1924). Meaning "station of a player in baseball" is from 1881. Graphics sense "space enclosed within borders and rules" is from 1929. Slang meaning "vulva" is attested 17c., according to "Dictionary of American Slang;" modern use seems to date from c. World War II, perhaps originally Australian, on notion of "box of tricks." Box lunch (n.) attested from 1899. The box set "multiple-album, CD or cassette issue of the work of an artist" is attested by 1955. To think or act outside the box "contrary to convention" is attested by 1994.