Age, eon (3)
I believe the answer is:
era
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">age</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(both can mean a long time)</span><br/ ><br/ >'<span class="explanation-format__original">eon</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for era that I've seen before include "Age marked by a distinctive character" , "Stage" , "Long period of history" , "quite some time" , "Specific time" .)