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heyday; golden age
彼は全盛期を過ぎたが、まだ戦える。
He's past his heyday, but he can still fight.
ローマ帝国は2世紀に全盛期を迎え、広大な領土を支配した。
The Roman Empire reached its golden age in the 2nd century and ruled vast territories.
あの会社の全盛期は終わった。
That company's heyday is over.