A bikini is usually a women's abbreviated two-piece swimsuit with a bra top for the chest and panties cut below the navel. The basic design is simple: two triangles of fabric on top cover the woman's breasts and two triangles of fabric on the bottom cover the groin in front and the buttocks in back. The size of a bikini bottom can range from full pelvic coverage to a revealing thong or G-string design.

The bikini is the most important thing since the atom bomb.
- Diana Vreeland

The name for the bikini design was coined in 1946 by Parisian engineer Louis Réard, the inventor of the bikini. He named the swimsuit after Bikini Atoll, where testing on the atomic bomb was taking place. Fashion designer Jacques Heim, also from Paris, invented a similar design in the same year. Due to its controversial and revealing design, the bikini was slow to be adopted. In many countries it was banned from beaches and public places. The Holy See declared the design sinful. While still considered risqué the bikini gradually became a part of popular culture when filmstars like Brigitte Bardot, Raquel Welch, Ursula Andress and others began wearing them on public beaches and in film.

Etymology and lexicon

While the two-piece swimsuit as a design existed in classical antiquity, the modern design first attracted public notice in Paris on July 5, 1946. French mechanical engineer Louis Réard introduced a design he named the "bikini", taking the name from the Bikini Atoll in the Pacific Ocean, where, four days earlier, the United States had initiated its first peace-time nuclear weapons test as part of Operation Crossroads. Réard hoped his swimsuit's revealing style would create an "explosive commercial and cultural reaction" similar to the explosion at Bikini Atoll.

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By making an inappropriate analogy with words like bilingual and bilateral containing the Latin prefix "bi-" (meaning "two" in Latin), the word bikini was first back-derived as consisting of two parts, [bi + kini] by Rudi Gernreich, who introduced the monokini in 1964. Later swimsuit designs like the tankini and trikini further cemented this false assumption. Over time the "–kini family" (as dubbed by author William Safire), including the "–ini sisters" (as dubbed by designer Anne Cole), expanded into a variety of swimwear, often with an innovative lexicon, including the monokini (also numokini or unikini), seekini, tankini, camikini, hikini (also hipkini), minikini, and microkini. The Language Report, compiled by lexicographer Susie Dent and published by the Oxford University Press (OUP) in 2003, considers lexicographic inventions like bandeaukini and camkini, two variants of the tankini, important to observe.