A later addition (12)
I believe the answer is:
afterthought
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">a later addition</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 afterthought that I've seen before include "not an original idea" , "Something added later" , "A reflection" , "footnote" , "Later addition" .)