bobtail

(noun) a short or shortened tail of certain animals. Synonyms: bob, dock.

(noun) large sheepdog with a profuse shaggy bluish-grey-and-white coat and short tail; believed to trace back to the Roman occupation of Britain. Synonyms: Old English sheepdog.

(adj) having a short or shortened tail. Synonyms: bobtailed. Example: "Bobtail mare."