"Eh up!", pants Spice Girl appearing halfway through Glee (8)
I believe the answer is:
euphoria
'glee' is the definition.
(thesaurus)
'eh up pants spice girl appearing halfway through' is the wordplay.
'pants' indicates anagramming the letters (UK informal term for 'nonsense' or 'rubbish').
'spice girl' becomes 'ori' (I can't justify this - if you can you should give a lot more credence to this answer).
'halfway through' indicates the central letters.
The central letter of 'appearing' is 'a'.
'eh'+'up'='ehup'
'ehup' anagrammed gives 'euph'.
'euph'+'ori'+'a'='EUPHORIA'
(Other definitions for euphoria that I've seen before include "transport" , "Ecstatic feeling" , "Blissful state" , "Great happiness and exhilaration" , "Rapture" .)