The term "hammered out deal" implies a robust and thorough negotiation that ends with an agreement. However, there are several antonyms that can describe a failed negotiation, such as "deadlock," "impasse," or "stalemate." These words suggest a situation where both sides are unable to come to an agreement. Other antonyms include "abandonment," "rejection," and "discord," which evoke a sense of disagreement or breakdown in communication. While "hammered out deal" suggests a positive outcome, the antonyms highlight the complexities and challenges that can arise during negotiations, reminding us that not all deals are successful.