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former; ex-; past; one-time
earlier times; the past; previous state
formerly; previously; originally; before
旧体制から新体制への移行だ。
It's a transition from the old system to the new.
旧来のやり方を見直す必要がある。
We need to review the old ways.
旧型のパソコンを新しくした。
I replaced my old computer with a new one.