A friar who served as an attendant at the gate of a monastery court. As a curtal dog was not privileged to hunt or course, so a curtal friar virtually meant a worldly-minded one.
“Some do call me the curtal Friar of Fountain Dale; others again call me in jest the Abbot of Fountain Abbey; others still again call me simply Friar Tuck.” —Howard Pyle: The Merry Adventures of Robin Hood, ii. p. 141.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894