Mesmerism (9)
I believe the answer is:
hypnotism
'mesmerism' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for hypnotism that I've seen before include "Production of sleep-like state in person" , "Mesmeric technique" , "I spy month (anag)" , "Practice of inducing sleep-like state" , "Practice of inducing trance-like state" .)