Muhammad said: "Huwwah" (darkness) is blackness, and that is why that which is intensely green is called "ahwa" (dark), because it tends toward blackness. "Al-Ghutha'" in the language of the Arabs refers to what you see on the surface of floodwater. It is said of it: "ghatha al-wadi yaghthi" (the valley gathered its debris) when it collects its "ghutha'". The singular of "ghutha'" is "ghutha'ah".