Oceanic ice (4)
I believe the answer is:
floe
'oceanic ice' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for floe that I've seen before include "Frozen piece of Arctic" , "Piece of ice at sea" , "Flat mass of sea ice" , "Floating flat mass of ice" , "Separated piece of ice on water" .)