Definition
A bathing costume is an older term for what is now commonly called a "swimsuit" or "bathing suit". It refers to clothing worn for swimming or bathing, often in a more formal or traditional style than modern swimwear. Think of it as a vintage version of a swimsuit. Bathing costumes were often made of wool or cotton in the past, before the invention of quick-drying synthetic fabrics. Nowadays, it may sound somewhat antiquated but still means the same thing.