What does callus mean?
A callus is a patch of toughened, thickened skin that develops where friction or pressure is repeatedly applied — on a carpenter's hands, a dancer's feet, or a guitarist's fingertips. In medicine, the word also names the bridge of new bone that knits together a fracture as it heals, while in botany it describes an unorganized mass of plant cells that forms over wounds or grows in tissue culture. Used as a verb, "to callus" simply means to develop such hardened growth. The word carries largely neutral connotations: a skin callus often signals diligent work or practice, even resilience. It derives from Latin callus, meaning hard skin, and shares its root with the unrelated-sounding adjective "callous," which describes emotional hardness rather than physical toughness — a pair of words worth distinguishing carefully in writing.
An area of thickened, hardened skin produced by repeated friction or pressure; also a mass of tissue formed over a healing bone fracture, or a mass of undifferentiated plant cells in botany.
"The surgeon noted that a firm callus had formed around the healed break."
Plural is "calluses" in general use; "calli" appears occasionally in scientific writing.
To form a callus, or to cause hardened tissue to develop on a surface or wound.
"Within weeks, the graft had callused over and begun to take hold."
"Calluses" is the standard English plural; the Latinate "calli" is rare and confined to some scientific usage.
"Her calluses were proof of countless hours at the climbing wall."
That tough patch on your fingertips after weeks of guitar practice isn't damage — it's your body engineering its own armor.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of callus
The word "callus" comes directly from Latin callus (also written callum), meaning hard or thickened skin. It entered English in the mid-sixteenth century, initially in medical contexts. It is related to the adjective "callous" and the noun "callosity," which share the same Latin root, though "callow" is not related despite a similar appearance.
Related word forms
How callus is actually used
Mostly neutral to technical in register; common in everyday speech for skin thickening and in medical or botanical contexts for healing tissue. The spelling "callous" should be reserved for the adjective describing insensitivity.
Easily confused with callus
"Callus" is the noun (or verb) referring to hardened skin or tissue, while "callous" is an adjective meaning emotionally insensitive or unfeeling.