This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
嵃 combines 山 (mountain) with 彥, which likely contributes the sound. The exact historical development is uncertain.
The mountain radical 山 suggests a connection to mountains or steepness, but the overall meaning is unclear.
For ゲン, imagine a steep mountain pass where a gate (ゲート, gēto) marks the entrance: the first syllable ゲ of ゲート cues ゲン.