According to Jerome, those who were unfamiliar with Jewish customs tried to pronounce the Hebrew letters as if they were Greek letters. The result was quite a howler: they pronounced YHVH as PIPI!
Hebrew Nuggets, Lesson 5: Abba (Part 1)
Abba is an Aramaic word meaning “the father.” This word was borrowed by Hebrew speakers and used in the sense of “Daddy.” In lesson five, the word Abba is used to teach another Hebrew letter.