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important; serious; crucial
valuable; precious
serious matter; major incident; matter of grave concern; crisis
great undertaking; great enterprise; great thing
safe; OK
「大事」 has another reading with different meanings.
健康が一番大事なことですよ。
Health is the most important.
彼の健康は大事だと思う。
I think his health is important.
大事に長く使ってください。
Please use it carefully.