The antonyms for "unfastened" are "fastened," "closed," "locked," "shut," "buttoned," "zipped," "sealed," "secured," "clasped," and "tightened." These words describe the opposite state of being of "unfastened," which means to be open, loose, or unsecured. When something is "fastened," it is firmly secured or stuck in place. A "closed" or "locked" object is inaccessible, while a "shut" one is not open. "Buttoned," "zipped," and "clasped" refer to clothing or bags that have been fastened for security. Similarly, "sealed" objects prevent anything from getting in or out, and "tightened" ones are held in place.