defile, mountain pass, gorge
陘 centers on a narrow, steep-sided passage through mountains: a defile, gorge, or mountain pass.
陘 combines the hill radical ⻖ with 巠, which likely contributes the sound. The hill radical suggests a geographical feature, fitting the meaning of a mountain pass or gorge.
The left side ⻖ represents a hill or mound, and the right side 巠 looks like a winding path through steep walls. Together they form a narrow mountain pass or gorge.
For ケイ, imagine a narrow gorge shaped like the letter K, and you say 'K, eh?' as you squeeze through: K-eh -> ケイ.