Search deeply (5)
I believe the answer is:
delve
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">search deeply</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 delve that I've seen before include "Dig - research deeply" , "Turn up - dig" , "Hollow" , "Make painstaking enquiries (into something)" , "Reach down and search" .)