sudden, unexpected
溘 centers on something happening abruptly and without warning: a sudden, unexpected event.
溘 combines 氵 (water) with 盍, which likely contributes the sound. The exact historical development of the meaning 'sudden' from these components is uncertain.
Water 氵 can rise suddenly and unexpectedly, like a flash flood. The right side 盍 looks like a container with a lid, suggesting something contained that bursts out without warning.
For コウ, imagine a sudden, unexpected cough: cough -> コウ, and the water splashes out abruptly.
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sudden (esp. of a person's death); unexpected