acanthosis,n.Path.|ækænˈθəʊsɪs|[f.acantho- + -osis.]Abnormal thickening of the prickle-cell layer of the epidermis. acanthosis nigricans, a form of this which is associated with darkening of the skin and hyperkeratosis in the affected areas (often a sign of an underlying carcinoma).1889inCent.Dict.1890S. Pollitzer in P. G. Unna et al.Internat.Atlas Rare SkinDis.IV. x. 1 (heading)Acanthosis nigricans.1929Brit.Jrnl.Dermatol. & Syphilis XLI. 122The skin shows some acanthosis and parakeratosis, with a very dense round-celled infiltration of the superficial half of the corium, with a slight excess of deposit of pigment.1966Wright & SymmersSystemicPath.II. xxxix. 1500/2The clinical picture of acanthosis nigricans is characterized by thickening and deep pigmentation of the skin of the flexures, with hyperkeratosis of the palms and soles, and areas of depigmentation and warty tumours elsewhere.1988Brit.Med.Jrnl.20 Feb. 547/1In psoriatic skin mitosis is reduced and acanthosis diminished.