Spirit of girl set poet off (11)
I believe the answer is:
poltergeist
'spirit' is the definition.
(I know that poltergeist is a type of Ghost)
'girl set poet off' is the wordplay.
'off' indicates anagramming the letters.
'girl'+'set'+'poet'='girlsetpoet'
'girlsetpoet' with letters rearranged gives 'POLTERGEIST'.
'of' is the link.
(Other definitions for poltergeist that I've seen before include "Mischievous ghost" , "Active ghost" , "Noisy spook" , "Mischievous spirit" , "disruptive presence" .)