Compromise is an agreement between two parties where, generally both give and take a little. In a compromise, neither party gets exactly what they want (their ultimate will), but an agreement is reached. The result is a substitution of wills by agreement, but is still the final (accepted) will of both parties.
If I want to eat Chinese food, but my friends want to eat Mexican, I can dig in my heels and go to the Chinese restaurant by myself, or I can compromise my will and go with them to the Mexican restaurant tonight so we can eat Chinese tomorrow.
The definitive difference between permissive will and compromised will is the agreement of the parties. Yahweh doesn't agree to the sinner's sin by permitting it. So, it isn't a compromise, it is simply His refraining from exercising His sinless perfect will.
