Decimal (6)
I believe the answer is:
metric
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">decimal</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 metric that I've seen before include "Relating to poetic rhythm" , "Non-Imperial system of measurement" , "Like the SI system" , "Like some feet" , "System using litre and gram as units" .)