Origin

The character combines a hole or cave opening (the radical 穴 at the top) with 屈, which suggests bending or being enclosed. Together these parts depict a hollow space deep within rock or earth — the kind of enclosed cavity where you might crouch down or where the passage bends inward. The lower component adds the sense of something deeply recessed or tucked away, reinforcing the idea of a cavern rather than just any opening. This compound-ideographic approach creates a visual and conceptual picture of what a cavern actually is: a hollow, enclosed space underground.