This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
蔳 is a rare character composed of 艹 (grass) on top and 清 below. The exact historical development is uncertain.
The kanji has no clear meaning, but visually it shows grass 艹 over clear water 清. Imagine a rare plant growing by a clear stream, its meaning as elusive as the plant itself.
For セン, picture a rare cent (coin) hidden among the grass 艹 by the clear water 清: cent -> セン, and the kanji remains mysterious.