This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
匨 combines the enclosure 匚 with 壯 inside. The exact historical development is uncertain, and the character is rare in modern Japanese.
The enclosure 匚 holds the component 壯, but without a clear meaning, picture a hidden container whose contents are unknown.
For ソウ, imagine a soul (ソウ) trapped inside the 匚 enclosure, hidden away.