flattering, glibness
諞 centers on speech that is smooth and insincere: flattering talk or glibness used to persuade or charm.
諞 combines 言 (speech) with 扁, which likely contributes the sound and may suggest a flat or smooth quality, giving the idea of smooth, flattering talk.
The left side is 言 (words), and the right side 扁 looks like a flat, smooth surface. Picture words that are so smooth and flat they slide right past your defenses—that's flattery.
For ヘン, imagine a hen clucking smooth, flattering words to get extra feed: hen -> ヘン, and her glib clucking is pure flattery.
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