Alexander Dyce, A General Glossary to Shakespeare's Works

curtal “dog,” THE MERRY WIVES OF WINDSOR, ii. 1. 98 ; THE COMEDY OF ERRORS, iii. 2. 144; THE PASSIONATE PILGRIM, 29. “Originally the dog of an unqualified person, which by the forest laws must have its tail cut short, partly as a mark, and partly from a notion that the tail of a dog is necessary to him in running. In later usage, curtail-dog means either a common dog, not meant for sport, or a dog that missed his game. It has the latter sense in this passage [that is, in the first of the above passages,—Hope is a curtal dog].” Nares's Gloss.