This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
嶃 combines 山 (mountain) with 斬, which likely contributes a phonetic element. The exact historical development is uncertain.
A mountain 山 beside 斬, a shape associated with cutting. Picture a steep, rugged mountain face that looks like it was cut sharply.
For サン, imagine the sun rising over the steep mountain: sun -> サン, and the mountain's sharp ridges catch the first light.