Later addition (12)
I believe the answer is:
afterthought
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">later addition</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 afterthought that I've seen before include "Item added later" , "footnote" , "Later addition" , "A reflection" , "Rider" .)