pot, pitcher, small-mouthed earthenware pot
甖 centers on a specific type of earthenware container: a pot or pitcher with a small mouth. The meanings are tightly focused on this vessel shape.
甖 combines 瓦 (earthenware) with 賏, which likely contributes the sound. The character is a phono-semantic compound for a type of clay pot.
The bottom 瓦 is a clay tile or earthenware, and the top 賏 looks like a pair of eyes (目) over a shell (貝), suggesting a decorated pot. Imagine a small-mouthed pitcher with eye-like patterns.
For オウ, picture an old earthenware pot that makes a deep 'oh' sound when you blow across its small mouth: 'oh' -> オウ.