Diatribe and charlatan entered English within half a century of each other, near the end of the 16th century and at the start of the 17th century. Diatribe is the older of the two words; its Greek ancestor meant "pastime, study, discourse," and when the Latin diatriba appeared as the English diatribe it had a neutral sense, meaning simply "a prolonged discourse or discussion."

That sense is now archaic, but a different version of diatribe came into English in the early 19th century, courtesy of the French spin on the Latin diatriba. This is the sense familiar to us today: "a bitter and abusive speech or writing."

The story of charlatan is a bit more colorful. In the early 16th century, quacks wandered through Italy, peddling medicines and treatments of doubtful value. Because the village of Cerreto seemed to produce so many of these unskillful practitioners of medicine, the name Cerretano, "inhabitant of Cerreto," came to mean "quack." Such quacks always have a ready line of glib talk to help them sell their wares. Thus, under the influence of the Italian ciarlare (to chatter), Cerretana was altered to ciarlatano, from which we got our English charlatan.