Noun | 1. | ichthyosis - any of several congenital diseases in which the skin is dry and scaly like a fish congenital disease, genetic abnormality, genetic defect, genetic disease, genetic disorder, hereditary condition, hereditary disease, inherited disease, inherited disorder - a disease or disorder that is inherited genetically xeroderma, xerodermia - a mild form of ichthyosis characterized by abnormal dryness and roughness of the skin |