elæodochon

from The Century Dictionary.

• noun The uropygial gland or rump-gland of a bird; the oil-gland, a kind of sebaceous follicle saddled upon the pope's-nose at the root of the tail.
• noun It is composed of numerous slender tubes or follicles, which secrete the greasy fluid, and the ducts of which, uniting successively in larger tubes, finally open by one or more pores, commonly upon a little nipple-like elevation. Birds press out a drop of oil with the beak, and dress the feathers with it, in the operation called preening. The gland is large and always present in aquatic birds, which have need of a waterproof plumage; it is smaller in land-birds, as a rule, and wanting in some. The character of the elæodochon, whether it be bare or surmounted by a circlet of feathers, distinguishes various natural groups of birds.