On the outside (8)
(Other definitions for exterior that I've seen before include "Foreign" , "Outermost" , "covering" , "Retire ox (anag)" , "Outside" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">on the outside</span>' is the definition.<br/ ><span class="explanation-format__explanation">(external means outside or on the exterior)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for external that I've seen before include "Belonging to the outside" , "abroad" , "Outer" , "Lying outside" , "Relating to the outside" .)