The term DECREASE THE TIGHTNESS OF can be solved by the crossword solution LOOSEN, which is a 6 letter word. LOOSEN is an action verb that means to make something less tight or to make something less strict. It is often used in reference to clothing, such as loosening a belt or loosening a tie. It can also be used in reference to rules or regulations, such as loosening restrictions or loosening a curfew. In general, it means to make something less strict or less tight.