More lean; paint additive (7)
I believe the answer is:
thinner
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">more lean</span>' is the first definition.<br/ ><span class="explanation-format__explanation">('thin' is associated in meaning with 'lean')</span><br/ ><br/ >'<span class="explanation-format__original">paint additive</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for thinner that I've seen before include "Leaner" , "Skinnier" , "Slenderer" , "Less fat" , "Finer; turps, e.g." .)