fast, quick, sudden
亟 centers on speed and immediacy: something happening fast, quickly, or suddenly.
亟 is an ancient character whose exact historical development is uncertain. It is often analyzed as combining 二 (two) with 口 (mouth) and 又 (hand), but the original meaning and component relationships are not clearly established.
The top 二 suggests urgency, the middle 口 is a mouth shouting, and the bottom 又 is a hand waving quickly. Together they paint a scene of sudden, fast action.
For キョク, imagine a sudden, quick shock that makes you jump: shock -> キョク, and the kanji captures that fast, sudden feeling.