Deter means to discourage. Many believe that the use of capital punishment deters people from committing murder. Others think that is hogwash.
From the Latin de meaning "away" and terrere meaning "frighten," deter means to frighten away. "Hopefully the idea of being expelled will deter kids from cheating in school." Teddy Roosevelt's foreign policy dictum "walk softly but carry a big stick" was meant to deter other countries from messing with the United States.