窞

A cavity or depression specifically in stone. This includes natural geologic hollows (weathered pockets, sinkholes), man-made excavations (quarry pits, cisterns, foundation sockets), and small-scale technical cavities (mortises, bored holes).

Primarily a noun ("pit," "hollow"), but may function as a verb (to hollow out stone; to carve a socket) or an adjective (pitted, concave, or hollowed).

Distinguished from generic terms for holes or pits (e.g., 坑, 穴) by the requirement of stony materiality.

Fanqie reading is 徒感 (suggesting a reading near //táng//). Due to rarity, be alert for regional variants in different editions of the text.

The presence of the 石 radical restricts the meaning to stony materiality.

The use of 窞 over more common terms like 坑 or 洞 is a deliberate specification of material; the "stony" nature of the cavity is likely significant to the passage.