The peak or most successful period of something or someone's life; the time when something was most popular or powerful.
From the 1500s-1600s interjection 'heyda' (an exclamation of excitement or surprise), possibly from German 'heida.' The noun developed meaning 'a time of excitement,' then evolved to mean 'prime time.' Origin is debated but likely Germanic.
It's peculiar that 'heyday' started as just an excited exclamation but somehow became the word for the best days of your life—like the exclamation itself embodied that peak excitement energy! No one really knows why this particular interjection stuck while thousands of others vanished.
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