起雾 (qǐ wù) is a verb meaning 'to become foggy' or 'for fog to form'—describing the natural process when water vapor condenses near the ground, reducing visibility. The character 起 (qǐ) means 'to rise' or 'to begin', while 雾 (wù) means 'fog' or 'mist'. Together, they literally convey 'fog rises/begins', capturing the onset of foggy conditions. This phrase is commonly used in weather reports, travel advisories, and everyday descriptions of outdoor environments.

It typically appears in the predicate position, often with time or location modifiers (e.g., 早上起雾了, 山上起雾了). Unlike nouns like 雾 (fog), 起雾 emphasizes the dynamic change—not the static presence of fog, but the moment it starts forming. It’s neutral in register and widely used across spoken and written Mandarin, especially in northern and central China where temperature shifts frequently cause morning fog.