How did the constant pi get its name?

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:

http://www.johndcook.com/blog/greek_letters/