Entry 2 senses · 2 variants Webster, 1913 Heyday /hādā/ · Hey·day · IPA /ˈheɪdeɪ/ interj. n. 01 interj. An expression of frolic and exultation, and sometimes of wonder. 1. An expression of frolic and exultation, and sometimes of wonder. 02 n. The time of triumph and exultation; hence, joy, high spirits, frolicsomeness; wildness. 1. The time of triumph and exultation; hence, joy, high spirits, frolicsomeness; wildness. “The heyday in the blood is tame.” — Shak. “In the heyday of their victories.” — J. H. Newman.