The word first appeared in the pages of TIME. It was an article on the Allied bombing of key industrial targets in Italy. The bombs used were called blockbusters because of their ability to destroy an entire city block.
With time, the word entered the American lexicon as a metaphor for something shocking and explosive.
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In the pages of TIME, blockbuster was used to describe surprising news. In 1943, TIME used the word to describe a movie. The critics called the film adaptation of Mission to Moscow "as explosive as a blockbuster."
Not long after, the word started to refer specifically to movies that were commercially successful. The word became associated primarily with popular entertainment in general and with the big-budget, high-impact Hollywood hits.
Eventually, the idea of a blockbuster movie became associated with summer action movies, especially after Steven Spielberg's thriller, Jaws, released in the summer of 1975.
When Star Wars came out two years later, blockbuster became a synonym for the summer blockbuster genre.