A thickened and hardened part of the skin or soft tissue, especially in an area that has been subjected to friction. After years of playing the guitar, he developed a callus on his fingertips.
A hard formation of tissue, especially new tissue formed over a wound. The callus on the tree's bark indicated where a branch had been removed.
A mass of bony or plant tissue that develops at the site of a fracture or wound as part of the healing process. The X-ray showed a substantial callus forming around the broken tibia.