prevent

(verb) keep from happening or arising; make impossible. Synonyms: forestall, foreclose, preclude, forbid. Examples: "My sense of tact forbids an honest answer." "Your role in the projects precludes your involvement in the competitive project."

(verb) stop (someone or something) from doing something or being in a certain state. Synonyms: keep. Examples: "We must prevent the cancer from spreading." "His snoring kept me from falling asleep." "Keep the child from eating the marbles."