\Hey"day`\, interj. [Cf. G. heida, or hei da, D. hei
daar. Cf. {Hey}, and {There}.]
An expression of frolic and exultation, and sometimes of
wonder. --B. Jonson.

\Hey"day`\, n. [Prob. for. high day. See High, and
{Day}.]
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.