heyday
noun /ˈheɪdeɪ/
  /ˈheɪdeɪ/
 [usually singular]- the time when somebody/something had most power or success, or was most popular synonym prime- In its heyday, the company ran trains every fifteen minutes.
- a fine example from the heyday of Italian cinema
- a picture of Brigitte Bardot in her heyday
 Word Originlate 16th cent. (denoting good spirits or passion): from archaic heyday!, an exclamation of joy, surprise, etc.