Got a question for y'all (hey, I live in NC now, so I'm allowed to say that now!) I have a student exploring the < spire > family, and she can't figure out why all the words she has found in that family retain the < s > from the Latin spirare, except for < expire >.  I know the < s > isn't needed phonologically, but it doesn't interfere with it either, and I thought retaining the etymological link was more important. I notice in the "70 Matrices" that the < ex- > prefix is left out. Any thoughts?