stuffed nose
齆 centers on nasal blockage: a stuffed nose, as from a cold or congestion.
齆 combines 鼻 (nose) with 邕, which likely contributes the sound and possibly the idea of blockage or obstruction. The exact historical development is uncertain.
The nose 鼻 is paired with 邕, which looks like a blocked passage. Picture the nasal cavity sealed off, causing a stuffed nose.
For オウ, imagine saying 'Oh!' when your nose is so stuffed you can't breathe: Oh -> オウ, and the sound comes out nasal and blocked.