This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
坅 combines 土 (earth) with 今, but the exact historical development is uncertain. It may have originally referred to a type of pit or hole, given the kun reading あな, but this is not well established.
The left side is earth 土 and the right side is 今 (now). Imagine digging a hole in the earth right now, but the meaning is uncertain.
For キン, imagine a king digging a hole in the earth: king -> キン, and the earth 土 is being dug now 今.