Translation guide
In Japanese, the most common word for 'bathing suit' is 水着 (mizugi). There are also specific terms for different styles, such as school swimsuits or bikinis.
bathing suit
The speaker wants to refer to a bathing suit or swimsuit in general, for any gender or age.
The standard, all-purpose word for swimsuit or bathing suit. Used for men's, women's, and children's swimwear.
I bought a new bathing suit.
I'll change into my swimsuit.
Literally 'sea-water wear'. A slightly more formal or old-fashioned term for a swimsuit, often used for women's swimwear. Less common in everyday speech.
I went to a swimsuit exhibition.
The speaker wants to refer to the specific type of swimsuit worn in Japanese schools, typically a one-piece with a name tag.
Refers to the standard swimsuit used in Japanese schools, usually a dark blue one-piece with a name tag area. Commonly used by students.
Write your name on your school swimsuit.
The speaker specifically means a two-piece bikini.
The loanword for bikini. Used exactly as in English.
Wear a bikini and go to the beach.
The speaker wants to refer to tight men's swimwear, like Speedos.
The speaker means loose-fitting men's swimwear, like board shorts.
In most everyday situations, 水着 (mizugi) is sufficient for any type of swimwear. You don't need to specify the style unless it's important.
海水着 (kaisuigi) is an older term and can sound dated or formal. Stick with 水着 in conversation.