dream, to dream, visionary, stupid
夣 centers on the realm of dreams and visions, often with a sense of unreality or foolishness. The meanings 'dream' and 'visionary' connect to the dream world, while 'stupid' likely arises from the idea of being lost in unrealistic fantasies.
夣 is an older or variant form of 夢, which originally depicted a person in bed with an eye emphasized, representing dreaming. The modern components ⺫ (eye-like), 冖 (cover), and 夕 (evening) are stylized remnants of that pictographic origin.
The top ⺫ looks like a wide-open eye, 冖 is a blanket, and 夕 is the evening. Picture yourself under a blanket at night, eyes wide open but seeing only the strange visions of a dream.
For ム, imagine a dream where you are mooing like a cow: moo -> ム, and the silly dream makes you feel stupid when you wake up.