* Old English Origins: The word itself comes from the Old English phrase "hāg dæg," which translates to "high day," referring to a holy day or festival.
* Evolution of Meaning: Over time, the meaning shifted from a specific day to a more general period of prosperity, success, or prime. This change probably happened because holy days were often times of celebration and abundance, and the word became associated with that feeling of peak joy.
* Figurative Language: The metaphorical use of "heyday" to refer to a person's prime or a period of flourishing developed further in the 16th century.
* Literary Influence: The expression became popularized in Shakespeare's works, where he used it to describe a period of great happiness or success.
In essence, the term "heyday" evolved from a specific religious concept to a more general, and even poetic, expression of a time of peak achievement and happiness. It reflects a shift in our understanding of time and how we remember and celebrate its moments of greatness.