Prime (6)
(Other definitions for amazon that I've seen before include "Net giant" , "S. America's longest river" , "Female warrior - parrot - South American river" , "Brazilian river" , "World's largest river" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">prime</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for heyday that I've seen before include "Peak or prime" , "Time of greatest popularity" , "Highest period in someone's career" , "Time of maximum prosperity" , "Boom time" .)
(Other definitions for grade a that I've seen before include "Top quality in alphabetic designation" , "Best quality" , "Top quality or classification" .)