callus

A hardened area of the skin (especially on the foot or hand) caused by repeated friction, wear or use.

The material of repair in fractures of bone; a substance exuded at the site of fracture, which is at first soft or cartilaginous in consistency, but is ultimately converted into true bone and unites the fragments into a single piece.

The new formation over the end of a cutting, before it puts out rootlets.

In orchids, a fleshy outgrowth from the labellum.

In grasses, a hardened extension from the base of a floret, which may or may not elongate and is often covered in hairs or bristles.

A shining area on the frons of many species of Tabanomorpha (horse flies and relatives).

To form such hardened tissue.