Noun
A kind of chair formerly used for punishing scolds, and also dishonest tradesmen, by fastening them in it, usually in front of their doors, to be pelted and hooted at by the mob, but sometimes to be taken to the water and ducked; -- called also a castigatory, a tumbrel, and a trebuchet; and often, but not so correctly, a ducking stool.
Source: Webster's dictionary