Powerful circular current (6)
I believe the answer is:
vortex
'powerful circular current' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for vortex that I've seen before include "Powerful circular current of water" , "Whirlpool current" , "Whirling fluid" , "Whirling motion" , "Engulfing swirl of e.g. whirlpool" .)