KanjiJLPT N2
Polish

grind, polish, scour, improve, brush (teeth)

Mnemonic

You wrap coarse hemp fibers tightly around a rough stone, then drag it back and forth to polish the stone's face until it gleams like a mirror. The hemp shreds away, but the stone grows smoother with every pass. Keep polishing—brilliance demands persistence!
Additional thoughts
Picture the texture of hemp rope grinding against gray stone, sparks of shine appearing with each stroke. Hemp on top, stone on bottom—just like the kanji's structure.
Quick recall
Rub hemp on stone to polish it to a mirror shine.

Details

The keyword for 磨 is polish. This kanji conveys the idea of grinding, rubbing, or polishing a surface to make it smooth and refined. It can refer to the physical act of polishing an object, such as sharpening a blade or buffing a surface to a shine, as well as the metaphorical sense of refining one's skills, character, or abilities through diligent effort and practice. The underlying concept is one of persistent friction or effort applied to achieve a state of greater smoothness, clarity, or perfection.
On'yomi
Kun'yomi
みが.く、す.る

Used in vocab