The antonyms for the word "most nailed" could be "least secure", "barely held", "mostly loose", or "uncertainly fastened". These antonyms imply a lack of stability, strength, or durability compared to the original term. The opposite of being "most nailed" could mean something that is prone to falling apart, collapsing, or failing. In other words, it could be a state of being unreliable, flimsy, or easily breakable. Therefore, it is important to choose the right words to describe the level of security or certainty of an object or situation.