Where does the expression “Dog’s Letter” come from and What does Dog’s Letter mean?

The surest proof that the letter R was not formerly sounded as “ah,” the approximate current pronunciation in parts of England, New England, and some of our Southern states, lies in the fact that, as Ben Jonson put it (1636):

“R is the dog’s letter, and hurreth in the sound, the tongue striking the inner palate, with a trembling about the teeth.”

That is, as still heard in the speech of Scotland, Ireland, and our Midwestern states, it resembled the snarl of a dog.