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to stop (doing); to cease; to desist; to drop; to lay off; to give up; to quit
「止す」 has another reading with different meanings.
医者に言われて甘いものを止した。
I quit eating sweets because the doctor told me to.
タバコを止すのは簡単ではない。
It's not easy to quit smoking.
彼は最近タバコを止している。
He has been refraining from smoking recently.