Fight, strive against (6)
I believe the answer is:
combat
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">fight</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(combat is a kind of fight)</span><br/ ><br/ >'<span class="explanation-format__original">strive against</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ ></span>
(Other definitions for combat that I've seen before include "Armed fighting" , "Fight, struggle or contest" , "Oppose" , "Fight - strive against" , "A fight or contest, sometimes mortal" .)