Old English sendan "send, send forth; throw, impel," from Proto-Germanic *sond- (source also of Old Saxon sendian, Old Norse and Old Frisian senda, Middle Low German and Middle Dutch senden, Dutch zenden, German senden, Gothic sandjan), causative form of base *sinþan, denoting "go, journey" (source of Old English sið "way, journey," Old Norse sinn, Gothic sinþs "going, walk, time"), from PIE root *sent- "to head for, go" (source also of Lithuanian siųsti "send;" see sense (n.)).
Also used in Old English of divine ordinance (as in godsend, from Old English sand "messenger, message," from Proto-Germanic *sandaz "that which is sent"). Slang sense of "to transport with emotion, delight" is recorded from 1932, in American English jazz slang.
"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 + Middle English sonde "that which is sent, message," from Old English sand, from sendan (see send (v.)).
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]