Old performer partially unconscious, in a trance (7)
I believe the answer is:
sinatra
'old performer' is the definition.
(Frank Sinatra)
'partially unconscious in a trance' is the wordplay.
'partially' indicates a hidden word.
'SINATRA' can be found hidden inside 'unconscious in a trance'.
(Other definitions for sinatra that I've seen before include "Francis Albert did it his way" , "Francis Albert, late lamented singer" , "Something of a strain for top crooner" , "Francis Albert ..., singer and actor" , "'Old Blue Eyes'" .)