Grim men seek to save Titanic (7)
I believe the answer is:
immense
'titanic' is the definition.
(I've seen this in another clue)
'grim men seek to save' is the wordplay.
'to save' indicates the answer is hidden within the clue (I've seen 'saving' mean this).
'IMMENSE' is hidden within 'grim men seek'.
(Other definitions for immense that I've seen before include "Massive" , "Huge, really great" , "Vast or enormous" , "Jumbo" , "Exceedingly large" .)