The term WHITE NUN can be broken down into two crossword solutions: SMEW (4 letters) and WHITE (5 letters). SMEW is a species of duck native to Eurasia, and is also known as the SMEW Duck. It is a small duck with a WHITE body and black head, and is often found in wetlands. WHITE is a color that is often associated with purity and innocence. In some religious contexts, it is used to represent holiness and piety, which is why it is often used to describe nuns.