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u·ro·py·gi·al gland(yo͝or′ə-pī′jē-əl, -pĭj′ē-)
A large gland at the base of a bird's tail that secretes an oil used in preening. Also called oil gland.
(Zoology) a gland, situated at the base of the tail in most birds, that secretes oil used in preening
u•ro•pyg′i•al gland`(ˌyʊər əˈpɪdʒ i əl)
a gland at the base of the tail in most birds that secretes an oily fluid used in preening.