The term 'sinker' can refer to several different things. In the context of a crossword puzzle, it could refer to a DOUGHNUT (8 letters), donut (5 letters), U-boat (5 letters), or pitched drop ball (15 letters). A DOUGHNUT is a type of pastry made from deep-fried dough and often covered in sugar or other sweet toppings. A donut is a variation of the DOUGHNUT, usually with a hole in the center. A U-boat is a type of submarine used by Germany during World War II. Finally, a pitched drop ball is a type of pitch in baseball where the pitcher throws the ball with a downward motion.