The opposite of "un-twists" would be "twists." This means to rotate something around its axis or to curl a flexible object like a rope or hair. Another antonym for "un-twists" could be "secures" or "fastens," which implies the process of holding something firmly in place. This could be applied to twisted wires or cables, to ensure they don't become untangled. Similarly, "tightens" can serve as an antonym, implying the process of making something firm or secure. In essence, the antonyms for "un-twists" fall in the category of holding or making something secure and stable.