How epidemios, meaning "on the people," became adapted to mean "that which circulates or propagates in a country" is a crucial question. This evolution occurred during the second half of the 5th century (450 BC-400 BC), a period of intense activity in Greek literature, particularly with the prolificacy of Sophocles. But while nosos or loimos were frequently used, epidemios was not. In the Perseus Digital Library (www.perseus.tufts.edu), a database that does not yet include Hippocrates' works, the adjective epidemios was used only 9 times, including 4 times in Homer, in the 489 major referenced Greek texts (≈4.8 millions words, 0.02 occurrences per 10,000 words). Its Doric variants epidamos and epidemos were used 3 times. In comparison, nosos (disease) was used 712 times in the Perseus database (1.47 occurrences per 10,000 words). The verb epidemeo was used 144 times, primarily during the 4th century and always meaning "to live in or return to one's own country." This lack of material makes accurately exploring the reasons for the semantic evolution across centuries difficult. In Oedipus Tyrannos, Sophocles qualified the sense of epidemios as it referred to reputation or fame; fame naturally spreads in a country. , "It is a fact that the disease was propagating in the country" (Epidemics, book I, chapter 3). Although Sophocles used epidemios once in that new sense, Hippocrates established a medical meaning for the term.