Fight, strive against (6)
I believe the answer is:
combat
I believe this is a double definition.
'fight' is the first definition.
(I know that combat is a type of fight)
'strive against' is the second definition.
(thesaurus)
(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" .)