The name of a particularly mischievous female poltergiest [German polter = noisy, racketing, geist = spirit]. Poltergiest activities are well known and extensively documented - the smashing of crockery and windows, noisy crashes and rappings, furniture falling over, and so on.
Modern researches tend to believe that poltergiest manifestations are rare in families which do not include a teenage girl or at least a pubescent boy, but Quicksilver may be the exception to the rule.
She has pestered people in various parts of the English-speaking world, and always leaves her 'trademark' in the form of a large Q scrawled in soap, lipstick, or crayon on a wall, mirror, or window. Her other characteristic is a tinkling laugh, loud enough to disturb a sleeper but intriguing rather than frightening.
Unlike other poltergiests she visits families without teenage children and is mischievous ranter than destructive. She plays such pranks as slamming every door in the house at midnight, turning on all the lights, turning all the clothes in a wardrobe inside out, and filling baths, sinks, and washbasins to overflowing. Luckily she never stays long enough with a family to become a real nuisance.