beauty of face
娟 centers on delicate, graceful beauty, especially of a woman's face. The given meaning "beauty of face" is the core idea.
娟 combines 女 (woman) with 肙, which likely contributes the sound and may relate to a small or delicate idea, fitting the meaning of facial beauty.
A woman 女 beside 肙, which looks like a small mouth 口 under a moon 月, suggests a delicate, moon-like beauty of face.
For エン, imagine an elegant woman with a beautiful face named En: En -> エン, and her beauty is the focus.
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graceful; slim and beautiful