Kate’s ultimate still Titanic (4)
I believe the answer is:
epic
'titanic' is the definition.
(thesaurus)
'kate's ultimate still' is the wordplay.
'ultimate' suggests the final letters (the last or ultimate letter).
'still' becomes 'pic' (short for picture).
The final letter of 'kate' is 'e'.
'e'+'pic'='EPIC'
(Other definitions for epic that I've seen before include "Impressive scope" , "blockbuster" , "Heroic narrative verse" , "Marathon" , "Long poem, book, film" .)