Ask HN: How did Y Combinator get its name?

I've often wondered why the incubator Y Combinator is called "Y Combinator". Obviously it has something to do with the fixed point combinator (http://en.wikipedia.org/wiki/Fixed_point_combinator), but after reading that, I fail to see the connection to the Y Combinator program.

Maybe I'm missing something completely obvious. Can anyone fill me in?