Something that is cool has a temperature which is low but not very low.

If it is cool, or if a place is cool, the temperature of the air is low but not very low.

Clothing that is cool is made of thin material so that you do not become too hot in hot weather.

Cool colours are light colours which give an impression of coolness.

When something cools or when you cool it, it becomes lower in temperature.

When a feeling or emotion cools, or when you cool it, it becomes less powerful.

If you say that a person or their behaviour is cool, you mean that they are calm and unemotional, especially in a difficult situation.

If you say that a person or their behaviour is cool, you mean that they are unfriendly or not enthusiastic.

If you say that a person or their behaviour is cool, you mean that they are fashionable and attractive.

If you say that someone is cool about something, you mean that they accept it and are not angry or upset about it.

If you say that something is cool, you think it is very good.

You can use cool to emphasize that an amount or figure is very large, especially when it has been obtained easily.

If you tell someone to cool it, you want them to stop being angry and aggressive and to behave more calmly.

If you keep your cool in a difficult situation, you manage to remain calm. If you lose your cool, you get angry or upset.

If you play it cool, you deliberately behave in a calm, unemotional way because you do not want people to know you are enthusiastic or angry about something.