n.

1. the quality of being at a refreshingly low temperature
   
   • the cool of early morning
2. great coolness and composure under strain;
   aplomb, assuredness, poise, sang-froid
   
   • keep your cool

v.

1. make cool or cooler;
   chill, cool down
   
   • Chill the food
2. loose heat;
   chill, cool down
   
   • The air cooled considerably after the thunderstorm
3. lose intensity;
   cool off, cool down
   
   • His enthusiasm cooled considerably

adj.

1. neither warm nor very cold; giving relief from heat
   
   • a cool autumn day
   • a cool room
   • cool summer dresses
   • cool drinks
   • a cool breeze
2. marked by calm self-control (especially in trying circumstances); unemotional;
   coolheaded, nerveless
   
   • play it cool
   • keep cool
   • stayed coolheaded in the crisis
   • the most nerveless winner in the history of the tournament
3. (color) inducing the impression of coolness; used especially of greens and blues and violets
   
   • cool greens and blues and violets
4. psychologically cool and unenthusiastic; unfriendly or unresponsive or showing dislike
   
   • relations were cool and polite
   • a cool reception
   • cool to the idea of higher taxes
5. (used of a number or sum)  without exaggeration or qualification
   
   • a cool million bucks
6. fashionable and attractive at the time; often skilled or socially adept
   
   • he's a cool dude
   • that's cool
   • Mary's dress is really cool
   • it's not cool to arrive at a party too early