bobtail
/ˈbɒbteɪl
/noun
A docked tail of a horse or dog.Also, unlike cheetahs and lions (which have long tails that help provide balance when the animals run) Smilodon had a bobtail.
Origin
Mid 16th century: probably from bob2 + tail1. It was originally recorded as a humorous term for a kind of broad-headed arrow, probably because it looked as though it had been cut short.