stone implement
磆 centers on a stone implement, likely a tool or object made of stone. The meaning is narrow and concrete, with no clear extended senses.
磆 combines 石 (stone) with 骨, which likely contributes the sound カツ. The character probably denotes a stone tool or object, but the exact historical development is uncertain.
The left side is 石 (stone), and the right side is 骨 (bone). Imagine a stone implement used to work bone, or a stone tool shaped like a bone.
For カツ, picture a stone implement used to cut: cut -> カツ, and the stone tool makes a clean cut.
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