trundletail

from The Century Dictionary.

• noun A curled or curly tail, as a dog's.
• noun A dog with such a tail. Formerly also grindletail.
• noun Also trindletail.

from the GNU version of the Collaborative International Dictionary of English.

• noun A round or curled-up tail; also, a dog with such a tail.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A dog with a rounded, curled-up tail.