This root comes from the Greek word "phusis", meaning "nature".
Here's how the word "physician" evolved:
* "phusis" (Greek): nature
* "physicus" (Latin): natural, pertaining to nature
* "physicus" (Late Latin): physician
* "physician" (English): a person who is qualified to practice medicine
So, essentially, a physician is someone who is knowledgeable about the nature of the body and how to treat its ailments.