dark
濛 centers on a state of darkness or obscurity, often associated with dim, misty, or drizzly conditions. The given meaning 'dark' captures this core idea of reduced visibility.
濛 combines 氵 (water) with 蒙, which likely contributes both sound and the idea of covering or obscuring, suggesting water-related dimness such as mist or drizzle.
Water 氵 combined with 蒙 (which can suggest covering) creates an image of a dark, misty drizzle that obscures vision: 濛 is darkness brought by fine rain.
For モウ, imagine a dark, misty moor where visibility is low: moor -> モウ, and the damp air matches the water radical 氵.