Maelstrom (6)
I believe the answer is:
vortex
'maelstrom' is the definition.
(I know that maelstrom can be written as vortex)
This is the entire clue.
(Other definitions for vortex that I've seen before include "Whirl of water or air" , "Whirling mass of wind or water" , "Whirlpool - whirlwind" , "Spinning mass of water or air" , "Whirlpool or the like" .)