hit, collide, knock into, sound
磕 centers on forceful impact: hitting, colliding, or knocking into something, often producing a sound from the strike.
磕 combines 石 (stone) with 盍, which likely contributes the sound. The stone radical suggests hitting or colliding with a hard object, producing a sound.
A stone 石 on the left and 盍 on the right: imagine two stones colliding with a loud crack, representing hitting and the resulting sound.
For カイ, picture a kite crashing into a stone wall: kite -> カイ, and the collision makes a loud sound.
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