When the word felon entered English in the 1200s, it didn't have the fancy definition of "someone sentenced to more than one year in prison or death" like it does today. Rather, it carried the much simpler and more extreme meaning of "evil-doer", sometimes even applicable to Satan himself. This comes from Old French felon, with essentially the same meaning but also connotations of "traitor". According to one theory, Felon is a derivative of Latin fellare, which means "to suck". How this change happened is quite interesting: because people regarded traitors and the Devil so poorly, the word was applied in a pejorative manner, implying that people like that suck a certain male appendage. Yes. the word felon is etymologically connected to fellatio. Beyond that, fellare is reconstructed as having come from the Proto-Indo-European word dhe, which meant "to suck" but in a much more wholesome way.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.