most compact (7)
I believe the answer is:
densest
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">most compact</span>' is the definition.<br/ ><span class="explanation-format__explanation">('dense' can be a synonym of 'compact')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for densest that I've seen before include "extremely thick" , "Most closely packed" .)