Risky business (4)
I believe the answer is:
spec
'risky business' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for spec that I've seen before include "On - means without a plan but with hope of success" , "Requirement" , "Bet" , "On - means on the chance of achieving something" , "Gamble (colloq.)" .)