crack, hazardous, steep
巇 centers on a dangerous break or gap in a steep place: a crack in a cliff that makes the terrain hazardous and precipitous.
巇 combines 山 (mountain) with 戲, which likely contributes the sound and the idea of a gap or dangerous opening. The exact historical development is uncertain.
The mountain 山 on the left and the complex 戲 on the right suggest a steep mountain with a dangerous crack. Picture a sheer cliff face split by a deep fissure.
For キ, imagine a key-shaped crack in the steep mountain: key -> キ, and the hazardous gap looks like a giant keyhole in the rock.