WordWeb Online

1. Keep from happening or arising; make impossible
   "Your role in the projects prevents your involvement in the competitive project"
   - forestall, foreclose, preclude, forbid
    
2. Stop (someone or something) from doing something or being in a certain state
   "We must prevent the cancer from spreading"
   - keep

Derived forms: prevents, preventing, prevented

See also: prevention, preventive

Antonym: let

Encyclopedia: Prevent