Seeing girl, is turned on (6)
I believe the answer is:
vision
'seeing' is the definition.
(thesaurus)
'girl is turned on' is the wordplay.
'girl' becomes 'vi' (**).
'turned' shows that the letters should be reversed in order.
'is' backwards is 'si'.
'vi'+'si'+'on'='VISION'
(Other definitions for vision that I've seen before include "Imagination" , "Sight of an apparition?" , "See 24" , "The faculty of sight, may be imaginative" , "ideal?" .)