The Chinese word **乌云** (*wūyún*, meaning "dark cloud" or "storm cloud") is a compound noun formed through semantic combination. The first character **乌** (*wū*) primarily means "black" or "dark," often implying a deep, dull blackness. The second character **云** (*yún*) means "cloud." When combined, they create a new meaning that is more specific than the sum of its parts: not just any dark-colored cloud, but specifically the thick, heavy, and often rain-bearing clouds that signal an impending storm. This formation follows a common modifier-head structure in Chinese, where **乌** describes the key attribute of the head noun **云**, resulting in a vivid and efficient metaphorical term often associated with gloom or misfortune.