Arithmetical operation (8)
I believe the answer is:
addition
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">arithmetical operation</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for addition that I've seen before include "Simple kind of arithmetic" , "Process of summation" , "Calculation of the sum of numbers" , "Arithmetical operation" , "Arithmetic calculation" .)