Unzip is an action that involves opening or removing the zip on a garment or object. There are a few different words that can be used as synonyms to describe the same action. One of them is 'unfasten,' which means to release something that is currently held together. Another is 'unlock,' which implies that something is secured and needs to be opened. 'Unbutton' can also be used as a synonym for 'unzip,' but this specifically refers to opening a button on clothing, rather than a zipper. Lastly, 'untie' can be used to describe the action of removing a knot or something that is tied together.