Work in three parts (7)
I believe the answer is:
trilogy
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">work in three parts</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for trilogy that I've seen before include "Three-volume work" , "series" , "Group of three linked works" , "Group of three novels, films, etc" , "Story in three parts" .)