My dictionary says that a revenant is a person who returns after a long absence or after death, hence a ghost or apparition. However, I have read a few critical works on folklore which state that a revenant is the actual body of one who has died, said body being able to move and to speak. Revenants often disappear at daybreak.

For example, in the ballad "Cruel Mother" in which a young woman kills her illegitimate twin babes, the babes appear as revenants and pronounce the penances she must make.

No doubt the old people in Hull were seeing something like that.