bikini; two-piece swimsuit
Refers to the swimwear, especially a two-piece swimsuit. Usually written in katakana.
I bought a new bikini.
She was wearing a bikini at the beach.
彼女は海で赤いビキニを着ていた。
She was wearing a red bikini at the beach.
Bikini Island; Bikini
Place-name use referring to Bikini Island; in ordinary writing it often appears as ビキニ島 when the geographical sense needs to be clear.
I checked the location of Bikini Island on the map.
She walked along the poolside in her bikini.
ワンピース refers to a one-piece swimsuit (or dress), the opposite style to the two-piece ビキニ.
arrival at ... · counter for suits of clothing · nth place (in a race) · counter for moves (in go)
Katakana form. No language of origin is specified. The word is conventionally written as ビキニ for both the swimwear and the place name.