Unfortunately sneaky about commercial (5)
I believe the answer is:
sadly
'unfortunately' is the definition.
(thesaurus)
'sneaky about commercial' is the wordplay.
'sneaky' becomes 'sly' (I've seen this before).
'about' indicates putting letters inside.
'commercial' becomes 'ad'.
'sly' placed around 'ad' is 'SADLY'.
(Other definitions for sadly that I've seen before include "Lamentably, unfortunately" , "Regrettably" , "Unhappily" , "I regret to say" , "Alas" .)