dream, visionary, wishful
梦 centers on the mental world of sleep and imagination: a dream, something visionary, or a wishful thought that feels unreal.
梦 is a simplified variant of 夢, which originally combined 目 (eye) with a component suggesting blurred vision, and 夕 (evening), indicating the dim light of dreams. The modern 梦 replaces the upper part with 林 (forest), likely as a simplification, but the historical connection to dreaming is through the older form.
At evening (夕), when the forest (林) grows dark, your mind wanders into dreams and wishful visions.
For ム, imagine a dream where you are a cow going 'moo' (ム) in a moonlit forest: the moo sound cues ム while you dream under the trees.