ergot рдХреНрдпрд╛ рд╣реИрдВ? ergot рдХреНрдпрд╛ рд╣реИрдВ? A fungus (Claviceps purpurea) that infects various cereal plants and forms compact black masses of branching filaments that replace many of the grains of the host plant.The disease caused by such a fungus.The dried sclerotia of ergot, usually obtained from rye seed and used as a source of several medicinally important alkaloids and as the basic source of lysergic acid.