1. hypertrophy of the corneous layer of the skin. 2a. any of various conditions marked by hyperkeratosis. 2b. a disease of cattle marked by thickening and wringling of the hide and formation of papillary outgrowths on the buccal mucous membranes, often accompanied by watery discharge from eyes and nose, diarrhoea, loss of condition, and abortion of pregnant animals, and now believed to result from ingestion of the chlorinated naphthalene of various lubricating oils.