Rotary motor (7)
I believe the answer is:
turbine
'rotary motor' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for turbine that I've seen before include "Type of engine with internal bladed rotor" , "Power generator" , "Machine producing power when water drives a rotor, for example" , "Rotary engine" , "Power-producing machine" .)