Opening commercial with sex appeal (4)
I believe the answer is:
adit
'opening' is the definition.
(thesaurus)
'commercial with sex appeal' is the wordplay.
'commercial' becomes 'ad'.
'with' means one lot of letters go next to another.
'sex appeal' becomes 'it'.
'ad'+'it'='ADIT'
(Other definitions for adit that I've seen before include "Taking passage" , "Mine-shaft" , "Horizontal mine passage" , "Mine entrance passage" , "Horiz. mine entrance" .)