Seeing that (5)
I believe the answer is:
since
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">seeing that</span>' is the definition.<br/ ><span class="explanation-format__explanation">(both can mean 'when considering...')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for since that I've seen before include "From that time one" , "in the past" , "Seeing that" , "Because; ago" .)