bowl
盂 centers on a bowl-shaped container, typically a deep dish or basin.
盂 combines 皿 (dish) with 于, which likely contributes a phonetic element. The character originally referred to a type of bowl or basin.
The bottom 皿 is a dish, and the top 于 looks like a lid or a handle. Together they form a bowl with a distinctive top.
For ウ, imagine a bowl so deep it echoes 'oooh' when you speak into it: oooh -> ウ.