postcard 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.

early 15c., "a playing card," from Old French carte (14c.), from Medieval Latin carta/charta "a card, paper; a writing, a charter," from Latin charta "leaf of paper, a writing, tablet," from Greek khartēs "layer of papyrus," which is probably from Egyptian. The form has been influenced by Italian cognate carta "paper, leaf of paper." Compare chart (n.). The shift in English from -t to -d is unexplained.

The sense of "playing cards" also is the oldest of the French word. The sense in English was extended by 1590s to similar small, flat, stiff pieces of paper. As "small piece of cardboard upon which is written or printed the name, address, etc. of the person presenting it," from 1795: visiting-cards for social calls, business-cards announcing one's profession. The meaning "printed ornamental greetings for special occasions" is from 1862.

Application to clever or original persons (1836, originally with an adjective, as in smart card) is from the playing-card sense, via expressions such as sure card "an expedient certain to attain an object" (c. 1560).

Card-sharper "professional cheat at cards" is from 1859. House of cards in the figurative sense "any insecure or flimsy scheme" is from 1640s, first attested in Milton, from children's play. To (figuratively) have a card up (one's) sleeve is from 1898. To play the _______ card (for political advantage) is from 1886, originally the Orange card, meaning "appeal to Northern Irish Protestant sentiment."

Cards are first mentioned in Spain in 1371, described in detail in Switzerland in 1377, and by 1380 reliably reported from places as far apart as Florence, Basle, Regensburg, Brabant, Paris, and Barcelona. References are also claimed for earlier dates, but these are relatively sparse and do not withstand scrutiny. [David Parlett, "A History of Card Games"]