luxuriant growth, extreme, reach
蔇 centers on something that has grown or extended to an extreme degree: lush, abundant growth that reaches far, or a state that has become extreme.
蔇 combines 艹 (grass/plant) with 既, which likely contributes the sound and may suggest the idea of something already fully developed or extreme. The exact historical development is uncertain.
The top 艹 suggests lush plant growth, and the bottom 既 looks like something already in place. Picture plants that have already grown to an extreme, reaching far and covering everything.
For キ, imagine a key unlocking a garden where plants grow to extreme, luxuriant sizes: key -> キ, and the key opens the gate to this overgrown place.
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