[autodidakto]

Actually I take it back! Ms. isn't short for "Miss". Miss (no period) used to be the default title for a woman, but now it's Ms. (pronounced as you say), and like Mrs. & Miss, derives from Mistress.

Good reading:

http://en.wikipedia.org/wiki/Miss#Use_as_a_title_.28honorifi...

http://en.wikipedia.org/wiki/Ms.