The period of greatest popularity, success, or power; prime.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "heyday" in a sentence
"He was a man no longer young, but in what we call the heyday of life, when our own people are so absorbed in making provision for the future that they may be said not to live in the present at all."
"I refer to the heyday of Pan-Arabism, personified by Egypt's dictator at the time, Gamal Abd Al-Nasser, who came to power in July 1952 as the leader of the "free officers"."
"While it still love Jet Li, i think his heyday is past and it wouldn't hurt Hollywood to have a look at some of the OTHER HK, Korean, Japanese action stars."