small jar, jug
甌 centers on a small container made of earthenware: a small jar or jug.
甌 combines 瓦 (earthenware) with 區, which likely contributes a phonetic element. The character refers to a type of earthenware vessel.
The left side 區 looks like a container with compartments, and the right side 瓦 is earthenware. Picture a small clay jar with sections inside.
For オウ, imagine an old small jar that you exclaim 'Oh!' when you find it: Oh -> オウ.