Most extensive (7)
I believe the answer is:
largest
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">most extensive</span>' is the definition.<br/ ><span class="explanation-format__explanation">('large' can be similar in meaning to 'extensive')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for largest that I've seen before include "Maximum" , "Superlatively extensive" , "Most substantial" , "Biggest" , "Extremely generous" .)