For this reason (5)
I believe the answer is:
hence
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">for this reason</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 hence that I've seen before include "In the future; begone!" , "Thus" , "From this time, or for this reason" , "It follows from that fact" , "As a consequence" .)