What is "uropygial"

Uropygial \U`ro*pyg"i*al\, a. [See Uropygium.] (Anat.) Of or pertaining to the uropygium, or prominence at the base of the tail feathers, in birds.

Uropygial gland, a peculiar sebaceous gland at the base of the tail feathers in most birds. It secretes an oily fluid which is spread over the feathers by preening.

a. (context ornithology English) Of or pertaining to the uropygium; on the rump.