noun
1. : decay in a log following closely the annual rings
2.
a. : a disease of sweet potatoes caused by a fungus ( Rhizopus stolonifer ) in which the roots are girdled by bands of dry rot
b. : a disease of potatoes caused by a bacterium ( Corynebacterium sepedonicum ) and characterized by browning of the ring of vascular bundles — called also ring disease
c. : brown rot 1c