ichthyosis UK /ˌɪk.θiːˈəʊ̯.sɪs/US /ˌɪk.θiˈoʊ̯.sɪs/ noun1 •Any of a group of genetic skin disorders characterized by dry, thickened, scaly skin.A well-marked case of pseudo-leprosy or ichthyosis, a scale-like affection of the skin, unsightly, obstinate, but possibly curable, and certainly non-infective. — 1926 formsichthyoses