uropygium

noun

uro·​py·​gi·​um ˌyu̇r-ə-ˈpī-jē-əm 

: the fleshy and bony prominence at the posterior extremity of a bird's body that supports the tail feathers

Word History

Etymology

New Latin, from Greek ouropygion, from ouro- ur- entry 2 + pygē rump

First Known Use

1771, in the meaning defined above