6 letters · 16 points in Scrabble
noun the period of greatest prosperity or productivity
originLate 16th century, from earlier heyda (1520s), as exclamation – compare hey, hei. Sense “period of success, vigor” is a respelling as heyday based on unrelated day (as “period of time”) – compare day in the sun.
Etymology from Wiktionary, CC BY-SA 3.0