wastebasket diagnosis
n.— «They think of fibromyalgia as a label given to patients with many painful physical complaints, but normal test results. This is commonly called a “wastebasket diagnosis” used when all the clearly definable diseases have been tested for and eliminated as possibilities.» —“New drug treats a questionable disease” by Terry Gaff FWDailynews.com (Kendallville, Indiana) Jan. 20, 2008. (source: Double-Tongued Dictionary)