The term "nails down" is a phrasal verb that means to determine or finalize something, often after much discussion or negotiation. Some antonyms for "nails down" could include "uncertain," "undecided," "inconclusive," "tentative," or "unsettled." These words suggest a lack of clarity or firmness in one's decision-making, as opposed to the definitiveness conveyed by "nails down." Other antonyms might include "abandons," "postpones," or "puts off," which indicate a delay or avoidance of making a decision. Whatever the specific antonym, it implies a different approach to decision-making, one that is less concrete and less committed.