Brass bound is a phrase that refers to something that is tightly bound or reinforced. The antonyms for this phrase could be loosely bound, unsecured or unfastened. Something that is loosely bound is not firmly held in place, and thus could easily come apart. Similarly, an unsecured object is not held firmly, and could be easily moved or shifted. Lastly, unfastened things have not been fixed in place, which also results in a loose or unstable state. These antonyms serve to illustrate the opposite of a tight, secure, and fixed object, as described by the phrase brass bound.