This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 茡 is uncertain. It visually combines the grass radical 艹 with 字, but the original semantic or phonetic role of these components is unclear.
The top grass radical 艹 and the bottom character 字 (character/letter) suggest a plant whose name is written with this character, but the exact meaning is unknown.
For シ, imagine a sheet of paper with the grass-like character 茡 written on it: sheet -> シ, and the character looks like grass on a letter.
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