SDI /ˌes diː ˈaɪ/ BrE AmE
abbreviation for the Strategic Defense Initiative; a military plan started in the US in 1983 and strongly supported by President Reagan for making special weapons that could destroy an enemy country’s ↑ missile s before they could reach the US. It is commonly known as ‘Star Wars’ because the plan was for a system of ↑ satellite s containing ↑ laser weapons that would destroy missiles from space. Many scientists believed that the plan was impossible to achieve. In the end, the plan never became reality.