Source : Webster's Revised Unabridged Dictionary (1913)

Uropygium \U`ro*pyg"i*um\, n. [NL., fr. Gr. ?, (corrupted form)
   ?; ? the end of the os sacrum + ? rump.] (Anat.)
   The prominence at the posterior extremity of a bird's body,
   which supports the feathers of the tail; the rump; --
   sometimes called pope's nose.

Source : WordNet®

uropygium
     n : posterior part of a bird's body from which the tail feathers
         grow