All epidemics are not alike, even as they all have the powers to threaten the public’s health, broadly defined.The latest coronavirus is one tough enemy of the people, as doctors of medicine will tell you. But there is another category of menace, no less frightening when you think about it, for which we will have to turn to the doctors of etymology who tunnel through the centuries seeking the origins of words.It turns out, the word “epidemic” hails from the Greek “demos” (population or…