urostyle

noun

uro·​style ˈyu̇r-ə-ˌstī(-ə)l 

: a long unsegmented bone that represents a number of fused vertebrae and forms the posterior part of the vertebral column of frogs and toads

Word History

Etymology

International Scientific Vocabulary ur- entry 2 + Greek stylos pillar — more at steer

First Known Use

1875, in the meaning defined above