The antonyms for the word "pinning down" can be varied, and it depends mainly on the context of its usage. Some possible antonyms for this expression could include the words "freeing," "liberating," "letting go," or "releasing." These terms imply that instead of restricting or confining something, the opposite action is taken, allowing something to move, flow, or thrive. "Pinning up" could also be an antonym for "pinning down," indicating a deliberate act of supporting, securing, or displaying something in a prominent or aesthetic way. The opposite meaning of "pinning down" can change depending on the situation, making it a versatile and context-driven concept.