How do you spell Callus

Available Definitions:
1)  n. - Same as Callosity
2)  n. - The material of repair in fractures of bone; a substance exuded at the site of fracture, which is at first soft or cartilaginous in consistence, but is ultimately converted into true bone and unites the fragments into a single piece.
3)  n. - The new formation over the end of a cutting, before it puts out rootlets.