The term 'became opaque' can be summarized by the crossword solution 'CLOUDED, ' which is a 7-letter word. Clouding is a process in which something becomes less transparent or more difficult to see through, making it appear opaque. This can happen to a variety of materials, such as glass, plastic, and even air. In the case of air, clouding occurs when particles such as dust, smoke, or water vapor are suspended in the atmosphere, reducing visibility.