Definition of "Callus" :
noun: (botany) an isolated thickening of tissue, especially a stiff protuberance on the lip of an orchid
noun: bony tissue formed during the healing of a fractured bone
noun: an area of skin that is thick or hard from continual pressure or friction (as the sole of the foot)
verb: form a callus or calluses
"His foot callused."
verb: cause a callus to form on
"The long march had callused his feet."