This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
呞 combines 口 (mouth) with 司, but the exact historical development and original meaning are uncertain.
The mouth 口 beside 司 might suggest a mouth involved in managing or directing, but without a clear meaning, it is best remembered as a rare character.
For シ, imagine a mouth 口 making a soft 'shh' sound to manage 司 a quiet room: 'shh' cues シ.