(Ca-dug'-an). A club of hair worn by young French ladies; so called from the portrait of the first Earl of Cadogan, a print at one time very popular in France. The fashion was introduced at the court of Montbéliard by the Duchesse de Bourbon.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Cadogan from Fact Monster: