I. ˈhāˌdā interjection
Etymology: from earlier heyda, alteration of hey (I)
archaic — used to express frolicsomeness, exultation, or sometimes wonder
II. noun
also heydey “
1. archaic : high spirits : frolicsomeness , wildness , joy
2. : a time of highest strength, vigor, or prosperity : acme
in the heyday of his power
Athens and Venice in their commercial heyday — David Riesman
during the heyday of the fur trade — Grace L. Nute