seed of job's tears, lotus seed
薏 refers to the seed of Job's tears, a grain-like plant, and by extension lotus seed, likely due to similar appearance or use.
薏 combines the grass radical 艹 with 意, which likely provides the sound. The character is used for plant names, specifically Job's tears and lotus seeds.
The grass radical 艹 sits above 意, like seeds growing from a plant. Think of the seeds of Job's tears or lotus seeds sprouting from the grass.
For ヨク, imagine a yoke made of Job's tears seeds: yoke -> ヨク, and the seeds are strung together like a yoke.
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coix seed (used in traditional Chinese medicine)