TACKS ON is a term that can be used to describe the action of adding something to an existing item. The term can be broken down into three different crossword solutions: ADDS (4 letters), APPENDS (7 letters), and ATTACHES (8 letters). ADDS is the most basic form of the term, meaning to put something with something else. APPENDS is a more specific form of the term, meaning to add something to the end of something else. Finally, ATTACHES is the most specific form of the term, meaning to fasten something to something else.