Callous with an O is an adjective meaning emotionally hardened — a callous remark. A callus without it is a noun: a patch of thickened skin. The metaphor is the same in both, but the spellings do different jobs.
The core difference
An adjective about feeling and a noun about skin.
- callous (adjective) — unfeeling: callous indifference.
- callus (noun) — hardened skin: calluses on his palms.
The shared image
Both come from Latin callus, hard skin. The emotional sense is metaphorical — someone callous has grown a thick skin. Knowing they are the same word makes the pair easier to hold apart, because the adjective is the figurative one and takes the extra O.
The verb
Callused means covered in calluses. Calloused is also used, and in figurative senses — a calloused attitude — is widely accepted. That overlap is why the pair resists a clean rule.
Frequently asked questions
Which spelling is the skin?
Callus, without the O.
Are the words related?
Yes — both from Latin callus, hard skin. The emotional sense is metaphorical.
Is calloused a word?
Yes, and it is widely used both literally and figuratively, which is why this pair has no perfectly clean rule.