This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
觘 combines 角 (horn) with 少 (few/little), but the exact historical development is uncertain. It may have originally referred to a type of horn vessel or implement, but this is speculative.
The left side is a horn 角, and the right side is few/little 少. Imagine a small horn spoon used for tiny portions, but remember the meaning is uncertain.
For ソウ, imagine a small horn spoon being used to serve soup: soup -> ソウ, though the reading is not tied to a clear meaning.