[L. juglans the walnut + -one.]
(Chem.) A yellow crystalline substance (C₁₀H₆O₃) resembling quinone, extracted from green shucks of the walnut (Juglans regia); -- called also nucin. Chemically, it is 5-hydroxy-1,4-naphthalenedione.

Webster 1913 Dictionary edited by Patrick J. Cassidy