heyday: [16] Etymologically, the -day of heyday has no connection with the English noun day, although it has come to resemble it over the centuries. Nor is hey- related to hay. Originally the word was heyda, an exclamation roughly equivalent to modern English hurrah. Probably it was just an extension of hey, modelled partly on Low German heida ‘hurrah’. Its earliest noun use (first recorded in the 1590s) was in the sense ‘state of exultation’; the influence of the day-like second syllable did not make itself felt until the mid-18th century, when the modern sense ‘period of greatest success’ began to emerge.
heyday (n.)
late 16c., alteration of heyda (1520s), exclamation of playfulness or surprise, something like Modern English hurrah, apparently an extended form of Middle English interjection hey or hei (see hey). Modern sense of "stage of greatest vigor" first recorded 1751, which altered the spelling on model of day, with which this word apparently has no etymological connection.
例文
1. In its heyday ，the company ran trains every fifteen minutes.
社は最盛期には15分おきに列車を出していた。
2.By the 80 s,punk rock had really had its heyday .
1980年代になると、パンクロックは全盛期になった。
3.The 19 th century was the heyday of steam railways.
19世紀は蒸気機関車の隆盛の時代だった。
4.The rooms are furnished and recreate the atmosphere of the castle 's medieval heyday .
部屋はすべて配置され、この城の中世全盛期の雰囲気を作り直した。
5.Docklands in its heyday was a major centre of industrial and commercial activity.