One plus one (3)
I believe the answer is:
two
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">one plus one</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 two that I've seen before include "1 + 1" , "Company, so it's said" , "Pair; hour after lunch" , "Even number" , "Old song 'Tea for . . .'" .)