'Physician' and 'physics' share the same root — Greek 'physis' (nature). A doctor literally 'knows nature.'
The branch of biology dealing with the normal functions of living organisms and their parts.
From Proto-Indo-European *bhuH- ("to be, to grow, to become") + *leg- ("to collect, to speak"), via Greek physiologia ("natural science, study of nature"), composed of physis ("nature, growth, natural constitution") + logos ("word, reason, account, study"). The Greek physis descends from phuein ("to grow, to bring forth"), from PIE *bhuH- — the same root as English be and been, Latin fui ("I was"), futurus ("about to be"). Greek logos descends from legein ("to gather, speak"), from PIE *leg- — the root of Latin legere (to