Also found in: Thesaurus, Medical, Financial, Acronyms, Idioms, Encyclopedia, Wikipedia. Marked by calm self-control: a cool negotiator. Of, relating to, cool valentines gifts for boyfriend characteristic of colors, such as blue and green, that produce the impression of coolness.

Knowledgeable or aware of the latest trends or developments: spent all his time trying to be cool. It’s cool if you don’t want to talk about it. To make less ardent, intense, or zealous: problems that soon cooled my enthusiasm for the project. To become less warm: took a dip to cool off.

To become calmer: needed time for tempers to cool. A cool place, part, or time: the cool of early morning. The state or quality of being cool. These adjectives indicate absence of excitement or discomposure in a person, especially in times of stress. Cool usually implies an alert self-possession, but it may also indicate aloofness: “Keep strong, if possible.