فالخفي: ما خفي المراد به بعارض لا من حيث الصيغة.
Khafī is expression whose intended application becomes hidden due to an incidental factor, not because the wording itself is obscure.
The ordinary linguistic sense remains evident. Difficulty appears when an unusual case is encountered: should that person or act be included within the legal designation? The obscurity concerns the special features of the case, not the lexical meaning of every part of the expression.
The interpreter first establishes ordinary usage, then examines whether the exceptional case satisfies the conditions for the ruling.