cup, pot, bowl, abundant
盎 centers on a container that holds liquid or food, like a cup, pot, or bowl. The sense of abundance comes from the image of a vessel filled to the brim.
盎 combines 皿 (dish, vessel) with 央, which likely contributes the sound and may suggest fullness or center. The character originally referred to a wide-mouthed vessel.
The top 央 looks like a person with a big belly, and the bottom 皿 is a dish. Imagine a person holding a large bowl filled to the brim, representing a cup or pot that is abundant.
For オウ, picture an overflowing bowl of soup making an 'ow!' sound when it spills: ow -> オウ, and the bowl is so full it's abundant.