n. In anatomy: Hard skin; a callosityn. A new growth of osseous tissue between and around the extremities of fractured bones, serving to unite them.n. In botany, any unusually hard excrescence upon a plant; also, the thickening of the substance of the perforated septa between sieve-cells, and the close cellular structure which is formed over wounds, by which the inner tissues are protected and healing is effected.n. In horticulture, the cap or thickening formed over the end of a cutting before it sends forth rootlets.n. In conchology, a callosity or indurated thickening of a shell by the deposit of some hard substance different from the rest of the shell.