Mathematical operation (8)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mathematical operation</span>' is the definition.<br/ ><span class="explanation-format__explanation">(addition is a kind of mathematical operation)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for addition that I've seen before include "plus" , "Calculation of the sum of numbers" , "Calculation of the sum of two or more" , "Something extra" , "an arithmetical process" .)
(Other definitions for minus that I've seen before include "Negative sign - negative thing" , "'Take away' sign" , "Lacking; negative" , "Reduced by the subtraction of - thus?" , "Less, without" .)