Why pain is called pain

I had this moment of epiphany when I was walking back tonight from my Krav Maga class tonight: "Pain is called pain because it hurts." I am hurting everywhere. My back, my legs, my arms, my knuckles (I did well with the punching bag). So anyway, I shared it on Facebook and I think although tautological it deserves to be a great unknown line. Rose is a rose is a rose, after all. And it works for all sorts of pains.