Earth neighbor (4)
I believe the answer is:
mars
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">earth neighbor</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for mars that I've seen before include "world" , "Fourth rock from the Sun" , "Holst's Bringer of War" , "March to the French" , "Next planet out" .)