The word ghost is a cognate of "guest," both words rooted in Germanic Geist, originally a spirit of a dead ancestor invited to tribal feasts on such occasions as Samhain (Halloween) and other solemn ceremonies.
Many European peoples preserved the heads or skulls of ancestors, which were set up, painted, and decorated, in a prominent position at gatherings of the clan, and were consulted for oracles after being offered their portion of the collation. Hence the "Death's-head at the feast."
During later Christian times the custom was discouraged, for the church's doctrine of resurrection of the flesh forbade burial of bodies without heads.
Nevertheless, the visiting ghost was an ineradicable belief. Ghosts were supposed to haunt all the scenes of their former lives, especially if they died violently or unhappily, or were buried in unconsecrated ground, or had possessed evil spirits. The earlier, more benevolent type of family ghost is still suggested by the identical pronunciation of "ghost" and "guest" in northern England.'
The anger of ghosts was most feared by people who refused to honor them as guests.
Source: Barbara G. Walker