In the word "Poltergeist", what is the meaning of the prefix "Polter"?

The subject of many books, films, and debates, the phenomenon known as a "Poltergeist" takes its name from two German words meaning "Noisy Ghost" (or "Noisy Spirit").

Poltergeist activity is said to manifest itself in loud noises, movement of furniture, and various mysterious knockings, rappings, and tappings. It is more generally associated with a person rather than a place, although some places do seem to be more prone to poltergeist activity.

There are any number of rational explanations for such phenomena, ranging from temperamental adolescents, to weather conditions, to confirmation bias.

The Poltergeist question was a bone of contention between the eminent psychoanalysts Carl Jung and Sigmund Freud, as the former was inclined to believe in some supernatural element, or at any rate a projection of his own subconscious, and the latter disagreed.

Incidentally, though now rarely used in its own right as a word in modern German "Polter" is also preserved in the word "Polterabend" - literally "Noisy Evening" - a stag night!