Furrow one's brow (5)
I believe the answer is:
frown
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">furrow one's brow</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 frown that I've seen before include "Scowl, look crossly" , "Indicate disapproval" , "Furrow one's brows" , "Facial expression of dislike or concentration" , "Dirty look" .)