post 3 
(pōst)
(pōst)n.
1. Chiefly British
a. A postal system.
b. A post office.
c. A delivery or amount of mail: waiting for the morning's post to arrive.
2. Obsolete
a. One of a series of relay stations along a fixed route, furnishing fresh riders and horses for the delivery of mail on horseback.
b. A rider on such a mail route; a courier.
v. post·ed, post·ing, posts
v.tr.
1. Chiefly British To mail (a letter or package).
2. Archaic To send by mail in a system of relays on horseback.
3. To inform of the latest news: Keep us posted.
4.
a. To transfer (an item) to a ledger in bookkeeping.
b. To make the necessary entries in (a ledger).
5. Computers To enter (a unit of information) on a record or into a section of storage.
v.intr.
1. Archaic
a. To travel in stages or relays.
b. To travel with speed or in haste.
2. To bob up and down in the saddle in rhythm with a horse's trotting gait.
adv.
Archaic
Archaic
1. With great speed; rapidly.
2. By post horse.
[French poste, from Old French, relay station for horses, from Old Italian posta, from Vulgar Latin *posta, station, from Latin posita, feminine past participle of pōnere, to place; see apo- in the Appendix of Indo-European roots.]