Deep in thought (7)
I believe the answer is:
pensive
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">deep in thought</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 pensive that I've seen before include "musing" , "in a brown study?" , "Deeply thoughtful" , "Introspective, maybe moody" , "Brooding" .)