a deficiency disease caused by a lack of nicotinic acid or its precursor tryptophan in the diet. It is characterized by dermatitis, diarrhoea, and mental disturbance, and is often linked to over-dependence on maize as a staple food.
early 19th century: from Italian, from pelle 'skin', on the pattern of podagra
pellagra in other Oxford dictionaries
Definition of pellagra in the US English dictionary