medicus

Medicus, medici is masculine, second declension. It is really an adjective, medicus, medica, medicum, "healing", that hardened into a noun; the feminine medica, a woman doctor, is attested and unremarkable.

Behind it sits medeor, a deponent verb meaning "I heal", which takes the dative: you heal to someone, not someone. The same root gives remedium and, through a different line, meditor and modus, all circling the idea of measuring and setting right. In Rome medicine was a Greek trade practised largely by freedmen and slaves, which is why Cato can sneer at doctors while Pliny records their fees; the social contempt is in the texts, not in the word. English medical, medicine and medic all come from it.