Once a warring Indian, perhaps (5)
I believe the answer is:
ocean
'indian perhaps' is the definition.
(Indian Ocean is an example)
'once a warring' is the wordplay.
'warring' is an anagram indicator.
'once'+'a'='oncea'
'oncea' anagrammed gives 'OCEAN'.
(Other definitions for ocean that I've seen before include "One of the Seven Seas" , "Large expanse of water" , "Large stretch of sea" , "Immense expanse or quantity" , "Large stretch of water" .)