Herculean (7)
I believe the answer is:
titanic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">herculean</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for titanic that I've seen before include "Ill-fated vessel" , "Colossal, liner" , "Act in it (anag.)" , "Nineteen twelve iceberg victim" , "Successful movie - disaster ship" .)