Where does “callōsus” come from?

callōsus (Latin) comes from Latin callum, from Proto-Indo-European kal — hard.

Ancestry of “callōsus”, step by step

Step	Language	Word	Meaning
1	Latin	callum	A hard or thick substance; The hardened, thick...
2	Proto-Indo-European	kal	hard

callōsus — Etymology, Origin & Word History | Etymology Explorer