This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 秖 is uncertain. It visually combines 禾 (grain) and 氏, but the original semantic and phonetic roles are unclear.
With no clear meaning, picture a grain stalk 禾 beside a family crest 氏, like an obscure symbol whose story has been lost.
For シ, imagine a single grain of rice (し) sitting on the family crest: し -> シ, a tiny sound for a forgotten kanji.