To deter someone from doing something means to make them not want to do it or continue doing it. Supporters of the death penalty argue that it would deter criminals from carrying guns Arrests and jail sentences have done nothing to deter the protesters = discourage. to stop someone from doing something, by making them realize it will be difficult or have bad results deterrent (deterrere, from terrere )
try to prevent; show opposition to; "We should discourage this practice among our youth