Other forms: impasses
When two huge semi trailers met face-to-face on a one-lane mountain road, the drivers jumped out of their cabs and exclaimed, "We're at an impasse! We can't move forward — we can only reverse and go back in the direction from which we came."
If you investigate impasse a little more closely, you'll discover passer, the French word for to pass. The im- prefix is a negative, meaning that there's no way any passing is going to occur. It's impossible. An impasse is any situation in which the parties involved can't, or won't, move forward or make any sort of progress. Either they are literally stuck, like two big trucks trying to pass each other on a narrow road, or they are figuratively stuck, as in two politicians who are unable to reach an agreement on a new policy.