Master, Main
The radical master and the kanji master have the same meanings! This kanji also means main because the master is the main person of a dojo or household or business.
しゅ
おも, ぬし, あるじ
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Do you remember back to the radical mnemonic, where the master is floating a water drop above his head? Imagine back to there. Once you do, the most amazing thing happens. The master sends the drop of water into a chute (しゅ) and it goes careening through an intricate series of them.
Picture this master of water controlling the droplet as it flies around inside these chutes, like he's solving a difficult puzzle with it. Astounding!