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.

Source: Webster's Revised Unabridged Dictionary (1913)