uropygial gland

noun

uro·​py·​gi·​al gland ˌyu̇r-ə-ˈpī-jē-əl- 

: a large gland that occurs in most birds, opens dorsally at the base of the tail feathers, and usually secretes an oily fluid which the bird uses in preening its feathers

called also oil gland

Word History

First Known Use

1870, in the meaning defined above