"... it takes a remarkable wizard to keep the elder wand for any length of time."
-- Mr. Ollivander (Pm)
Elder is a tree from which wandmakers take wand wood (Pm).
Elder is "the rarest of wand woods and "trickiest to master" (Pm). It has long been considered bad luck, according to the old saying "wand of elder, never prosper," but Mr. Ollivander disagreed with that superstition (Pm). Ron, however, says his mother Molly taught him the same old saying, which he passed along to Hermione and Harry (DH21). Dumbledore repeated in his notes on Beedle the Bard (TBB).
According to Dumbledore, other names for elder include "Ellhorn" and "Eldrun" (TBB).
The legendary Elder Wand in the Tale of the Three Brothers has been called the "Wand of Destiny" and the "Death Stick" (TBB, DH21, DH32). Historical owners include Antioch Peverell (DH21), Emeric the Evil, Egbert, Godelot and his son Hereward, Barnabas Deverill, and the evil Loxias (possibly killed by his own mother) (TBB). According to Mr. Lovegood, either Arcus or Livius took the wand from Loxias (DH21).
The wand-maker Gregorovitch possessed it, but it was stolen from his workshop by Gellert Grindelwald, who subsequently lost it to his old friend Dumbledore in a duel in 1945 (PS6,DH24). Dumbledore possessed the Elder Wand until his death and recognized it as one of the Deathly Hallows.
Draco Malfoy disarmed Dumbledore just before his death on the Astronomy Tower and received the loyalty of the wand, even though Snape performed the Avada Kedavra moments later. The Elder Wand remained loyal to Draco even after it was buried with the Headmaster(HBP27). Voldemort killed Grindelwald in prison, after which he stole the wand from the white tomb, without ever being recognized as master by the wand itself (DH23,DH24). When Harry wrestled away Draco's wand at Malfoy Manor, the wand changed loyalty again, this time to Harry (DH23). When Harry came into the forest to sacrifice himself, the Elder Wand refused to kill him and backfired on Voldemort (DH34).
Old English ellæn, ellærn "elderberry tree"
A fast-growing shrubby plant, the elder can be used as an instant hedge. Both the berries and flowers of the elderberry have been eaten as jam or made into wine-like beverages for thousands of years. However, the raw uncooked berries and juice can be poisonous, as are other parts of the plant, due to the presence of cyanide. Possibly this is why the elder tree was considered to be bad luck sometimes. source: Wikipedia