Stripped nut just spins around on my starter?

If i turn in the tighten position it just spins. And if I try to turn it in the loosen position it just spins around, Basically stuck in one spot. It's on my cars starter bolt( the Bigger one that the battery cable connects to on the solenoid) How can i get this off? I tried a wrench and it just spins around both way and goes no ware