Japanese seaweed is flipping smooth (4)
I believe the answer is:
nori
'japanese seaweed' is the definition.
'flipping smooth' is the wordplay.
'flipping' shows that the letters should be reversed in order.
'smooth' becomes 'iron' (I've seen this before).
'iron' reversed gives 'NORI'.
'is' acts as a link.
(Other definitions for nori that I've seen before include "seaweed" , "oriental food" , "Japanese food" .)