Exhort is a 15th-century coinage. It derives from the Latin verb hortari, meaning "to incite," and it often implies the ardent urging or admonishing of an orator or preacher. English speakers apparently took to the root hort, fiddling around with different prefixes to create other words similar in meaning to exhort. They came up with adhort (meaning the same as exhort) and dehort (a word similar to exhort and adhort but with a more specific meaning of "to dissuade"). Adhort all but vanished after the 17th century. Dehort had a slightly better run than adhort, but it is now considered archaic.