This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 倧 is uncertain. It combines 亻 (person) with 宗, which may have contributed sound, but the original meaning is unclear.
A person 亻 beside 宗 (a shape associated with religion or ancestors) suggests a possible connection to a person in a ritual role, but the meaning is not confirmed.
For ソウ, imagine a person 亻 at a solemn ceremony 宗, softly chanting 'sou' as a prayer: sou -> ソウ.
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