Common cowboy nickname (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">common cowboy nickname</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for slim that I've seen before include "insufficient" , "Elegantly thin or slender" , "Bakery produce" , "Svelte" , "Annual horse race" .)