This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 蒒 is uncertain. It visually combines the grass radical 艹 with 師, but the original semantic and phonetic roles are unclear.
With the grass radical 艹 above 師, you might imagine a teacher (師) hidden among tall grass, but the true meaning is uncertain.
For シ, picture a teacher (先生, せんせい) standing in the grass: the シ from せんせい cues the reading, though the kanji's meaning remains unclear.