Disease. Definition. noun, plural: diseases. An abnormal condition of an organism which interrupts the normal bodily functions that often leads to feeling of pain and weakness, and usually associated with symptoms and signs.elated terms: Wagners disease, Wolmans disease, hoof-and-mouth disease. Please contribute to this project, if you have more information about this term feel free to edit this page. This page was last modified on 29 September 2008, at 07:15.This page has been accessed 110,385 times.