‘暗沟’ literally means ‘hidden ditch’ — 暗 (àn) means ‘dark’, ‘hidden’, or ‘concealed’, and 沟 (gōu) means ‘ditch’, ‘trench’, or ‘channel’. Together, they refer to a covered or underground drainage channel built to carry water, sewage, or storm runoff — what English calls a ‘culvert’ or ‘covered drain’. These structures are typically made of concrete, brick, or metal and lie beneath roads, sidewalks, or building foundations.

‘暗沟’ is commonly used in urban planning, civil engineering, and infrastructure maintenance contexts. Unlike open ditches (明沟), which are visible on the surface, 暗沟 is intentionally concealed for safety, aesthetics, and efficiency. It appears in technical documents, municipal reports, and construction discussions — rarely in casual conversation unless describing flooding, drainage problems, or renovation work. The term carries a neutral, formal register and is standard across mainland China and Taiwan.