E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Whip-dog Day.
October 18 (St. Lukes Day). Brand tells us that a priest about to celebrate mass on St. Lukes Day, happened to drop the pyx, which was snatched up by a dog, and this was the origin of Whip-dog Day. (Popular Antiquities, ii. 273.)