Zahir, nass, mufassar and muhkam mark grades of textual clarity. They are not interchangeable names: the intended meaning and remaining scope for alternative interpretation differ.
Zahir indicates a meaning clearly, even if that meaning is not the primary purpose of the speech. Nass is brought particularly to establish its stated meaning. Mufassar is further clarified; muhkam carries the strongest form of settled indication.
Their counterparts—khafi, mushkil, mujmal and mutashabih—likewise involve different difficulties: application, competing meanings, lack of clarification or profound inaccessibility.
Simply labelling a text “clear” or “unclear” misses the legal significance of these specific categories.