A cloudbank is a thick mass of cloud, often low, that looks like a wall or a long pile in the sky. From the ground it can look as if a grey hill of cloud is sitting on the water or on the land. Pilots and weather people use it; ordinary people use it too when the sky seems to hold one solid block of cloud rather than little separate ones. You may also see it written cloud bank. Bank here does not mean a place for money. It means a piled-up mass, the same idea as a snowbank.