Middle English senden, from Old English sendan "dispatch (as a messenger, on an errand); order or cause to go or pass (from one place to another);" also "send forth, emit; throw, propel, cause to be delivered or conveyed."

This is reconstructed to be from Proto-Germanic *sond- "make to go" (source also of Old Saxon sendian, Old Norse senda, Old Frisian senda, Middle Low German and Middle Dutch senden, Dutch zenden, German senden, Gothic sandjan), causative form of *sinþan "to go, journey" (source of Old English sið "way, journey," Old Norse sinn, Gothic sinþs "going, walk, time"). This in turn is from the PIE root *sent- "to head for, go" (source also of Lithuanian siųsti "send"), for which see sense (n.). For the linguistic connection of "go" and "sense," compare German sinnen (past tense sann) "go over in the mind, review, reflect upon." 

The meaning cause (someone) to go into some specified state (send to sleep, etc.) is by 1831. The slang sense of "to transport with emotion, delight" is by 1932, in American English jazz slang. To send word "transmit or dispatch a message" (to someone) is from c. 1200. To send for "summon, send a message or messenger for" is by late 14c.

"a farewell" (especially a funeral), 1872 ("Mark Twain"), from the verbal phrase send off "cause to be sent" (attested by 1660s), from send (v.) + off (adv.). Earlier a send-off was "a start," as on a journey or race (1841), hence "a display of good-will on the occasion of such."

"a spoof; action of mocking or teasing," by 1958, slang, from the verbal phrase send up "to mock, make fun of" (1931); see send (v.) + up (adv.). This is perhaps a transferred use of the public school colloquial phrase for "to send a boy to the headmaster" (usually for punishment), which is attested from 1821. In U.S. slang, send up could mean "convict of crime and imprison" (1852), and in 19c. nautical language it meant "hoist (a mast or yard) into its place aloft."

To send down (v.) also was a British university punishment: "compel a student to leave the college for a time" (1853), and in U.S. slang this also meant "put in prison" (1840).

alternative past tense and past participle of send, attested from late 14c.

also re-send, "to send back or again," 1550s, from re- "back, again" + send (v.). Related: Resent; resending.

c. 1200, "one who bestows something;" mid-15c., "person who sends (someone) on a mission;" agent noun from send (v.). In telegraphy, "a transmitter of a message," also the person transmitting it, by 1863. In 1930s slang, a popular musician or song, from the jazz slang sense of the verb. Sendee is recorded from 1806.

"unlooked-for acquisition or good fortune," 1812, earlier "a shipwreck" (from the perspective of people living along the coast), by 1806, from Middle English Godes sonde (c. 1200) "God's messenger; what God sends, gift from God, happening caused by God," from God + send (n.) "a message, a message," literally "that which is sent," from Middle English sonde, from Old English sand, the noun associated with sendan (see send (v.)). The spelling was conformed to the verb in later Middle English.

The common people in Cornwall call, as impiously as inhumanely, a shipwreck on their shores, "a Godsend." [Rev. William Lisle Bowles, footnote in "The Works of Alexander Pope," London, 1806]

"to send forth, throw or give out," 1620s, from Latin emittere "send forth," from assimilated form of ex "out" (see ex-) + mittere "to send" (see mission). Related: Emitted; emitting.

early 15c., demitten, "to run or flow down," also figurative, "to humble oneself," from Old French demetre "to send, put, or let down," and directly from Latin demittere "to send down," from de "down" (see de-) + mittere "to release, let go; send, throw" (see mission).