from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The period of greatest popularity, success, or power; prime.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A period of success, popularity or power; prime.
  • interj. A lively greeting.

from the GNU version of the Collaborative International Dictionary of English

  • n. The time of triumph and exultation; hence, joy, high spirits, frolicsomeness; wildness.
  • interj. An expression of frolic and exultation, and sometimes of wonder.

from The Century Dictionary and Cyclopedia

  • An exclamation of cheerfulness, surprise, wonder, etc.
  • n. Highest vigor; full strength; acme.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. the period of greatest prosperity or productivity


Perhaps alteration of heyda, exclamation of pleasure, probably alteration of Middle English hey, hey.
(American Heritage® Dictionary of the English Language, Fourth Edition)
Late 16th century, from earlier heyda (1520s), as exclamation – compare hey, hei. Sense “period of success, vigor” from 1751, which respelt as heyday based on unrelated day (as “period of time”) – compare day in the sun. (Wiktionary)



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