Herculean (7)
I believe the answer is:
titanic
'herculean' is the definition.
(thesaurus)
This is all the clue.
(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" .)