Long narrow hilltop (5)
I believe the answer is:
ridge
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">long narrow hilltop</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 ridge that I've seen before include "Brow" , "Long raised band" , "Raised strip between two furrows" , "Long narrow crest" , "Crest - reef" .)