giant radish, daikon
蔔 centers on a large, thick root vegetable: the giant radish or daikon. The meanings are specific to this plant rather than a broad conceptual cluster.
蔔 combines the plant radical 艹 with 匐, which likely provides the sound. The character was created to name the daikon radish, but the exact historical development of the phonetic component is uncertain.
The grass top 艹 sits above 匐, which looks like a container. Picture a giant radish growing under the grass, its thick root filling the space like something packed tightly.
For フク, imagine a giant radish so big it makes you say 'fook!' in surprise: fook -> フク, and the daikon is enormous.
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