Ten years (6)
I believe the answer is:
decade
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ten years</span>' is the definition.<br/ ><span class="explanation-format__explanation">(a decade is ten years)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for decade that I've seen before include "Period of ten years" , "Group of ten things" , "Ten-year span" , "Ten year period" , "The 1960s, for example" .)