Unfastener is a term that refers to an object or device which loosens or releases something that has been sealed or secured. The word can be replaced by synonyms such as opener, unlocker, untier, detach-er, and unbuttoner. An opener can refer to a tool that opens cans, bottles, or jars. An unlocker is a device that releases or opens locks or doors. An untier is used to untie knots or loosens ropes, threads, and strings. A detach-er removes something that has been fastened or attached. Lastly, an unbuttoner is used to undo button fastenings. These interchangeable words provide an easier and more descriptive way to describe something that unfastens or releases something else.