Every once in a while, I will be defining a common medical or biological term which sounds like it was devised by Martians. It wasn’t. The Greeks are usually to blame.

pyrexia: fever.

The word comes to the English language via modern Latin, itself having scooped up the word purexis from the Greek. The root pur- means fire. It is the same root that is used in the words “pyrotechnic” and “pyromaniac”. A patient with a fever is said to be “pyretic”.