crevice, interstice
郤 centers on a narrow opening or gap: a crevice or interstice, the small space between things.
郤 combines 谷 (valley) with ⻏ (a form of 邑, settlement). The exact historical development is uncertain, but the character likely originally referred to a place name or a narrow valley-like opening.
The left side 谷 is a valley, a natural gap in the land. The right side ⻏ looks like a small enclosed space. Together they suggest a narrow crevice or interstice, like a tiny valley between two surfaces.
For ゲキ, imagine a narrow crevice so tight it makes a squeaky 'geki' sound when you try to squeeze through: geki -> ゲキ.
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