The Collaborative International Dictionary
Rumpless
Rumpless \Rump"less\, a. Destitute of a rump.
Wiktionary
rumpless
a. Destitute of a rump.
Wikipedia
Rumpless
Rumpless is a term used for the mutation which causes the tail of an animal to be absent. Usage and examples can be found in Manx cats, Manx Rumpy, Belgian d'Everberg and Araucana chickens.