Our favorite itty-bitty swimsuit didn't get a proper name until the 1940s, but historians say the two-piece bathing staple actually has roots as far back as Ancient Rome where 4th-century mosaics depict gymnasts adorned in separate tops and bottoms. Despite the early introduction, flesh-exposing female clothing went out of favor for much of modern history, and swimming uniforms in the early 20th century were about as modest and all-concealing as you can imagine.
Slowly, however, well-known women made waves by wearing less and less to the beach, and by the 1940s, screen sirens like Rita Hayworth, were showing off a once-scandalous strip of flesh above their belly buttons. During that time, when the world was acutely aware of nuclear lingo, attractive women were commonly called "bombshells" and anything of intensity was referred to as "atomic."
It's no wonder, then, that when two separate two-piece swimsuit designs debuted in France in the summer of 1946, one was named the "atome." The second, designed by Louis Reard, hit the scene on July 5, 1946, just four days after the United States started atomic testing at the Bikini Atoll. Reard figured it was highly appropriate to call his design "le bikini," and the name stuck [source: Turner].