Treaty subject (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">treaty subject</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 arms that I've seen before include "See 12" , "International competition for weapons" , ". . . . and the Man (G B Shaw) (4)" , "Supplies weapons" , "George Bernard Shaw play '. . . . and the Man'" .)