Sources: WHO, Indian Journal of History of Science, Encyclopaedia Britannica, US Centers for Disease Control and Prevention, Historic UK, Ancient History Encyclopedia, history.com, The Journal of Interdisciplinary History, aztec-history.com Sabyasachi Kundu
Epidemic, the word, as we understand it now, is the widespread occurrence of a disease in a community at a particular time. Pandemic relates to the geographic spread of an epidemic. The term epidemic is 2,500 years old and is a compound of the Greek terms epi meaning on and demos meaning people. The word epidemios was used by Homer in Odyssey, to describe someone who has returned home or to his country. Thucydides used the term epidemeo as a verb to mean “to stay in one’s own country”, as opposed to apodemeo, “to be absent from one’s country”. Later, orators Demosthenes and Aeschines used this word to refer to a stranger who arrived someplace with the intention of living there. Authors before Hippocrates used epidemios for almost everything from persons to rain to rumours to wars, but not diseases. Hippocrates was the first to adapt this word as a medical term. In the 5th century BC, the Greek physician wrote the seven-volume Epidemics, wherein he used epidemios to mean “that which circulates or propagates in a country”.
Source: A 2006 paper — 2,500-year Evolution of the Term Epidemic by Paul M.V. Martin and Estelle Martin-Granel