Formal work (8)
I believe the answer is:
treatise
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">formal work</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for treatise that I've seen before include "Written work dealing with one subject" , "Disquisition" , "Formal piece of writing on a particular subject" , "A written work about treaties" , "Learned written work" .)