Gradual deterioration is a process in which something deteriorates over time. It can refer to physical objects, such as buildings or machines, or it can refer to abstract concepts, such as relationships or beliefs. In the context of this crossword, the term can be broken down into two words: WEAR and EROSION. WEAR is a four-letter word that refers to the gradual damage caused by friction or use over time. EROSION is a seven-letter word that refers to the gradual destruction of something due to natural forces, such as wind or water. Together, these two words describe the process of gradual deterioration.