This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 窻 is uncertain. It likely combines 穴 (hole/cave) with a phonetic component, but the original meaning and component relationships are unclear.
The top 穴 suggests a hole or opening, and the bottom 悤 looks like a busy mind (公 over 心). Imagine a window or opening that lets thoughts escape, but remember the meaning is uncertain.
For ソウ, imagine a soul (ソウ) peeking through a small opening in a cave: soul -> ソウ, and the opening is the uncertain window.