Wiktionary
n. a silicone, latex or Lycra cap worn on the head by recreational and competitive swimmers.
Wikipedia
A swimming cap, swim cap or bathing cap, is a tightly fitted, skin-tight garment, commonly made from silicone, latex or lycra, worn on the head by recreational and competitive swimmers.
Caps are worn for various reasons. Some facilities require the wearing of swim caps, in order to protect filters from becoming clogged with loose hairs which fall from the head of swimmers who are not wearing a cap, or to ensure long loose hair does not get caught in equipment. Caps are also sometimes worn in an attempt to keep hair relatively dry or protect from chlorinated water, to keep the sun off the hair, and also, when a cap is worn with ear plugs, in order to keep water out of the ears. Competitive swim caps also reduce drag in the water caused by loose hair. During longer swimming sessions, a swim cap keeps the wearer's head warm. In some countries swimming caps are required before entering the swimming pool, this is often the case in Italy and Hungary.
Usage examples of "swim cap".
The room echoes flatly, and four little girls are huddled in the water on the other side of the pool, swearing to each other in whispers that they have seen me in the dressing room without my swim cap and my green-tinted goggles.
She changed first in our cottage named Alicia, and came out in a narrow bikini that was a froth of rows of crisp horizontal white ruffles, and by the time I got up to the pool she was swimming, wearing a swim cap covered with vivid plastic daisies.
Cindy Lewis scampered across the concrete deck of the pool, tucking her unruly blond hair under her swim cap.