Eastern firm set up by an Indian, perhaps (5)
I believe the answer is:
ocean
'indian perhaps' is the definition.
(Indian Ocean is an example)
'eastern firm set up by an' is the wordplay.
'eastern' becomes 'e'.
'firm' becomes 'co' (a firm is a company).
'set up' says the letters should be written backwards.
'by' means one lot of letters go next to another.
'co' written backwards gives 'oc'.
'e' after 'oc' is 'oce'.
'oce'+'an'='OCEAN'
(Other definitions for ocean that I've seen before include "Indian perhaps" , "Sea - canoe (anag)" , "Very large area of sea" , "A mighty sea" , "Indian or Arctic, say" .)