noun
Etymology: flag (I)
1. : a smut of cereal and other grasses that chiefly affects the leaves and stems and is characterized by formation of linear chains of sori within the plant tissues which later rupture releasing black masses of spores and causing fraying of affected areas ; especially : such a disease of wheat caused by a smut fungus ( Urocystis tritici )
2. : a smut fungus causing flag smut