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."