A disincentive makes you not want to do something. The possibility of getting an expensive ticket is one disincentive for speeding on the highway.
Use the noun disincentive to mean something that discourages you from taking some action, instead of motivating you to try the way an incentive does. A library fine is a disincentive from keeping books for too long, and the fear that you'll be rejected is a disincentive from applying to a competitive college. The Latin prefix dis is key here: it means either "a lack of" or "do the opposite of."