X-disease

Etymology
From the convention of using "X" as a variable to stand for something unknown.

Proper noun

 * 1) Any of various diseases of plants or animals whose origin was at first a mystery, especially:
 * 2) Hyperkeratosis in cattle.
 * 3) A disease of stone fruits caused by a form of mycoplasma.
 * 1) A disease of stone fruits caused by a form of mycoplasma.
 * 1) A disease of stone fruits caused by a form of mycoplasma.
 * 1) A disease of stone fruits caused by a form of mycoplasma.
 * 1) A disease of stone fruits caused by a form of mycoplasma.