It's always a good idea for a math tutor to know everything (it's almost like being a mother!) Yesterday a student asked me why π [the mathematical constant] is named with the Greek letter π. Of course I didn't know offhand, though I guessed that since π had an important connection with the perimeter of a circle, that somebody along the way decided to use the Greek letter for "p" as the name for the constant. I was mostly correct, as it turns out, but the actual history is much more interesting...
Read more here:
William Jones and his Circle: The Man who Invented Pi
p.s. While writing this post, I found this: