Terrain; touch down (4)
I believe the answer is:
land
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">terrain</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">touch down</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(eg touch down in a plane)</span><br/ ><br/ ></span>
(Other definitions for land that I've seen before include "See 22" , "Light" , "See 3" , "nation" , "Bring or come ashore" .)