The term 'Makes Watertight' can be solved by two crossword solutions: 'CAULKS' (6 letters) and 'Seals' (5 letters). Caulking is a process of filling and sealing joints or seams in various structures and materials, such as in the hulls of boats. It is usually done with a flexible material, such as silicone, that can be applied in a liquid form and then hardens. Sealing is a similar process, but it typically involves using a more rigid material, such as rubber, to fill gaps and prevent water from entering. Both caulking and sealing are used to make objects watertight.