transitive. spec. To shorten (the tail of a horse, dog, etc.) by cutting off one or more of the extreme caudal vertebræ. Also absol.

To make a curtal of by docking the tail; to dock. Obsolete.

transitive. To make an incision at the root of (a horse's tail) in order to make the animal carry it higher; to cut (a horse) in this way…

To dock, cut short (a horse's tail, etc.). Also with off. ? U.S.