Real Dictionary

ergot in American English
the hard, reddish-brown or black, grainlike masses (sclerotia) of certain parasitic fungi (esp. genus Claviceps) that replace the kernels of rye or other cereal plants
noun: a disease of rye and other cereal grasses, caused by a fungus of the genus Claviceps, esp. C. purpurea, which replaces the affected grain with a long, hard, blackish sclerotial body

ergot in British English
noun: a disease of cereals and other grasses caused by ascomycete fungi of the genus Claviceps, esp C. purpurea, in which the seeds or grain of the plants are replaced by the spore-containing bodies (sclerotia) of the fungus

ergot in the Pharmaceutical Industry
noun: Ergot is a substance obtained from a type of fungus, which is the source of certain alkaloids used to treat hemorrhage and facilitate contraction of the uterus in childbirth.