This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development is uncertain. The modern form combines 亻 (person) with 事, but the original semantic and phonetic roles are unclear.
A person 亻 beside 事 (matter, thing) could suggest a person involved in some matter, but the exact meaning is unclear.
For シ, imagine a person 亻 handling a matter 事 with a simple 'shh' sound, as if quietly taking care of business: shh -> シ.