Dig (into) (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">dig into</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 delve that I've seen before include "Look closely (into)" , "Rummage deep (in)" , "Dig up - search" , "Search deeply for information" , "Reach down and search" .)