This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
媙 combines 女 (woman) with 威, which likely contributes sound. The exact historical development is uncertain.
A woman 女 beside 威, a shape associated with authority or dignity, suggests a dignified or beautiful woman, but the exact meaning is unclear.
For イ, imagine a beautiful woman saying 'ee' (イ) in admiration of her own elegance.