a kind of water plant
蒻 refers to a specific kind of water plant. The meaning is narrow and concrete, without broader abstract extensions.
蒻 combines the grass radical 艹 with 弱, which likely contributes a phonetic element. The character is used for a specific water plant, but the exact historical development is uncertain.
The grass top 艹 sits above 弱, which looks like two bows 弓 with ice 冫. Picture a weak, bowing water plant growing among grass.
For ジャク, imagine a weak water plant that can't stand up straight: it's a 'jack' of all trades but master of none, so it just floats weakly. Jack -> ジャク.
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konnyaku (Amorphophallus konjac); konjac; devil's tongue
titan arum (Amorphophallus titanum); corpse flower; carrion flower
ragfish (Icosteus aenigmaticus)
fruit jelly (gelled with konjac starch); fruit jello
Japanese book size (approx. 12.5cm by 17.5cm)