But it does have a surprising relationship with the English calm.
Both come from the Latin cauma, which means “the heat of the sun in the middle of the day”. (What a specific concept! We need an English word for the same!). Cauma comes from the Latin calere, “to be hot.”
Thus, the word for heat has turned into, in English, the word for tranquility: calm! The heat, indeed, does calm us down!
We can see the pattern clearly if we map the root c-l of calor to the c-l of calm. The silent “l” in calm makes this less obvious than it should be!