Vortex (4)
I believe the answer is:
eddy
'vortex' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for eddy that I've seen before include "Swirling current" , "She founded Christian Science in 1866, d. 1910" , "Spinning current" , "Swirl; Duane -, US guitarist" , "moving water" .)