Titanic battle, shower wiped from terrain (7)
I believe the answer is:
monster
'titanic' is the definition.
(thesaurus)
'battle shower wiped from terrain' is the wordplay.
'battle' becomes 'mons' (Battle of Mons, WW1 battle).
'shower' becomes 'rain' (rainfall).
'wiped from' indicates named letters should be taken away.
'terrain' with 'rain' removed is 'ter'.
'mons'+'ter'='MONSTER'
(Other definitions for monster that I've seen before include "Large or legendary beast" , "Imaginary beast" , "eg Nessie" , "Ogre, demon" , "Beast - on terms (anag)" .)