Weighty work (4)
I believe the answer is:
tome
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">weighty work</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 tome that I've seen before include "A hefty book" , "Large, weighty book" , "Hefty volume" , "Large and scholarly book" , "Heavy volume" .)