Period, age (3)
I believe the answer is:
era
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">period</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that era is a type of period)</span><br/ ><br/ >'<span class="explanation-format__original">age</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(both can mean a long time)</span><br/ ><br/ ></span>
(Other definitions for era that I've seen before include "Epoch, period" , "Important historical period" , "Distinct period in history" , "A particular period of time" , "8" .)