This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
屻 combines 山 (mountain) and 刃 (blade). The exact historical development is uncertain, but it likely relates to a mountain peak or ridge.
A mountain 山 with a blade 刃 on its side suggests a sharp, jagged peak. Imagine a mountain ridge so sharp it could cut.
For ジン, picture a sharp mountain peak piercing the sky like a giant pin: pin -> ジン, and the mountain's blade-like edge is the pin.