Snooping in casino systems (4)
I believe the answer is:
nosy
'snooping' is the definition.
(thesaurus)
'in casino systems' is the wordplay.
'in' says the answer is hidden in the clue.
'NOSY' is hidden within 'casino systems'.
(Other definitions for nosy that I've seen before include "lots of questions" , "Inquisitive in nasal manner" , "Over-inquisitive" , "Meddlesome" , "Fragrant" .)