Decimal base (3)
I believe the answer is:
ten
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">decimal base</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ten that I've seen before include "Very young" , "X-WORD" , "time" , "Cardinal number" , "Half a score" .)