callus

Concise Oxford English Dictionary © 2008 Oxford University Press:
callus /ˈkaləs/ (also callous)

▶noun

• 1 a thickened and hardened part of the skin or soft tissue, especially one caused by friction.

• 2 Medicine the bony healing tissue which forms around the ends of broken bone.

• 3 Botany a hard formation of tissue, especially new tissue formed over a wound.

– origin C16: from L. callum, callus ‘hardened skin’.