Question: Where does the saying "what a bombshell" come from? 

Answer: The earliest I have heard it used was by Bob Hope in describing the buxom movie stars that toured with him during World War II as he and his troupe visited the U. S. soldiers in Europe and I think in the Pacific islands. Every G.I. saw a beautiful girl that would literally "blow his mind", and the girls' boobs when they wore lowcut dresses or revealing blouses looked like bombs with their rounded shapes.
This question from the Yahoo Q&A forum is categorized in the topic: Entertainment & Music