盛時|せいじseiji[1]atamadaka (head-high)

1. nounprime of life; era of national prosperity

• Synonym最盛期さいせいきNeutralThe period of greatest vigor; also the peak season for produce, as in 「出荷の最盛期」. The default word for a golden age.
• Synonym花盛りはなざかりNeutralFlowers in full bloom; figuratively a boom in popularity, as in 「人気花盛り」. 「盛時」 is more written in flavor and means a prime era.
• Synonym真っ盛りまっさかりNeutralColloquial. Right at the height of something, as in 「夏真っ盛り」; leans toward seasons rather than eras of prosperity.
• SynonymピークNeutralLoanword for a peak, often a numerical one, as in 「ピークを過ぎる」; leans toward values and graphs rather than prosperous times.
• Synonym盛りさかりNeutralThe time when something is at its height, as in 「働き盛り」; common in everyday speech.
• Synonym全盛ぜんせいWrittenWritten/formal prose. Full prosperity, as in 「全盛を誇る」; leans toward power or influence at its height.
• Synonym黄金時代おうごんじだいNeutralA golden age; leans toward a glorious period in history or culture rather than a personal or organizational prime.
• Synonym高潮こうちょうNeutralEmotions or excitement reaching a climax; also means high tide. Unlike 「盛時」, it tracks surging feeling, not a flourishing era.
• Synonym全盛期ぜんせいきNeutralThe heyday of a person, organization, or nation, as in 「全盛期の実力」; more colloquial than 「盛時」.
• Related頂点ちょうてんNeutralThe highest point or top, as in 「業界の頂点」; leans toward a place or position, while 「盛時」 points to a period of time.
• Related絶頂ぜっちょうWrittenWritten/formal prose. A peak or zenith of condition, as in 「人気の絶頂」; stresses a state of being at the top rather than the period itself.
• Related最高潮さいこうちょうNeutralThe moment excitement or atmosphere reaches its highest, as in 「盛り上がりが最高潮」; a peak of intensity, not a flourishing era.
• Related高潮こうちょうNeutralEmotions or excitement reaching a climax; also means high tide. Unlike 「盛時」, it tracks surging feeling, not a flourishing era.
• RelatedクライマックスNeutralLoanword for the climax of a story, as in 「物語のクライマックス」; the dramatic high point, not a period of prosperity.
• Related盛りさかりNeutralThe time when something is at its height, as in 「働き盛り」; common in everyday speech.
• Related山場やまばNeutralColloquial. The critical, decisive moment, as in 「交渉の山場」; leans toward a turning point rather than a flourishing period.
• Related真盛りまさかりWrittenWritten/formal prose. Means the same as 「真っ盛り」—right at the height—but is rarely used.
• Antonym末期まっきWrittenWritten/formal prose. The final stage near an end, not necessarily a decline; roughly opposite to 「盛時」 in the order of stages.
• Antonym衰退期すいたいきNeutralA period of decline; the direct opposite of the flourishing era that 「盛時」 denotes.

For a golden age or heyday, use 「全盛期」 or 「最盛期」. 「盛時」 is a written word for the prime years of a nation, organization, or person, as in 「盛時の面影」. For a climax, say 「クライマックス」; for the final stage, 「末期」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 血気けっき盛さかんな時期じき、年頃としごろ。
2. 国運こくうんやある組織そしきの勢力せいりょくなどが盛さかんな時期じき。