mid-12c., "authorized representative of the Pope," from Old French legat and directly from Latin legatus "ambassador, envoy," originally "provided with a commission," past participle of legare "send as a deputy, send with a commission, charge, bequeath," possibly literally "engage by contract" and related to lex (genitive legis) "contract, law," from PIE root *leg- (1) "to collect, gather." General sense of "ambassador, delegate, messenger of a state or authority" is from late 14c. in English. Related: Legator; legatee; legatine.
1901, "to play table tennis," from ping-pong (n.). In the figurative sense of "move or send back and forth without progress, resolution, or purpose" from 1952. Related: Ping-ponged; ping-ponging.
1610s, "action of delegating" (earlier in this sense was delegacie, mid-15c.); perhaps a native formation, perhaps from French délégation, or directly from Latin delegationem (nominative delegatio) "assignment, delegation," noun of action from past-participle stem of delegare "to send as a representative," from de "from, away" (see de-) + legare "send with a commission," possibly literally "engage by contract" and related to lex (genitive legis) "contract, law," from PIE root *leg- (1) "to collect, gather." Meaning "persons sent by commission" is from 1818; meaning "a state's elected representatives, taken collectively," is U.S. political usage from 1828.
"send by post," 1828, American English, from mail (n.1). "The usual word in the U.K. is still post" [OED]. Related: Mailed; mailing; mailable. Mailing list "register of addresses" is attested from 1876.
"person sent on a mission," 1620s, from French émissaire (17c.) or directly from Latin emissarius "a scout, a spy," literally "that is sent out," from emissus, past participle of emittere "send forth" (see emit).
Old English apostol "messenger," especially the twelve witnesses sent forth by Jesus to preach his Gospel (Luke vi.13), from Late Latin apostolus, from Greek apostolos "messenger, envoy," literally "person sent forth," from apostellein "send away, send forth," from apo "off, away from" (see apo-) + stellein in its secondary sense of "to send," from PIE *stel-yo-, suffixed form of root *stel- "to put, stand, put in order," with derivatives referring to a standing object or place. Compare epistle.
The current form of the word, predominant since 16c., is influenced by Old French apostle (12c., Modern French apôtre), from the same Late Latin source. Meaning "missionary who brings Christianity to a new region or people" is from early 15c. Figurative sense of "chief advocate of a new principle or system" is from 1810. The New Testament book title Apostles (c. 1400) is short for "The Acts and Epistles of the Apostles."