deterrent

Serving to deter, preventing something from happening.

Something that deters.

• An extension of the system to serve new housing estates on the outskirts of the city, at an estimated cost of about £4,000,000 a mile, is being considered, but the narrow gauge, small clearances, and short platforms are deterrents.
• Along with trial by ordeal, hanging was the most effective deterrent that could be devised in an age without police or prisons.