This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 谸 is uncertain. It visually combines 千 and 谷, but the original semantic or phonetic role of these components is unclear.
With no clear meaning, picture a thousand (千) valleys (谷) stretching into the distance, suggesting vastness or emptiness.
For セン, imagine a thousand (千, せん) valleys echoing the sound 'sen': 千 -> セン, tying the reading to the left component.