I. interjection Etymology: irregular from hey Date: 1599 archaic — used to express elation or wonder II. noun Date: 1590 high spirits, the period of one's greatest popularity, vigor, or prosperity
HEYDAY
Meaning of HEYDAY in English
Merriam Webster. Explanatory English dictionary Merriam Webster. Толковый словарь английского языка Мерриам-Уэбстер. 2012