good-looking, quiet
姶 centers on a woman who is good-looking and quiet, suggesting a graceful, composed beauty rather than a loud or flashy one.
姶 combines 女 (woman) with 合, which likely contributes the sound and may suggest a harmonious or fitting quality, leading to the idea of a good-looking, quiet woman.
A woman 女 who fits 合 in perfectly with her surroundings, being both good-looking and quiet.
For オウ, imagine a good-looking, quiet woman named Ou (pronounced like 'oh') who blends in harmoniously: Ou -> オウ.