Fond, Fool, or White Plough. The plough dragged about a village on Plough Monday. Called white, because the mummers who drag it about are dressed in white, gaudily trimmed with flowers and ribbons. Called fond or fool, because the procession is fond or foolish- not serious, or of a business character.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Plough from Infoplease: