Airstrip (6)
I believe the answer is:
runway
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">airstrip</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 runway that I've seen before include "Strip on which planes take off and land" , "Strip at the airport" , "A plane takes off from it" , "Landing surface" , "Airstrip" .)