Merriam-Webster's Collegiate® Dictionary, 11th Edition
COOL
I. adjective see: cold Date: before 12th century moderately cold ; lacking in warmth,
2. marked by steady dispassionate calmness and self-control , lacking ardor or friendliness , marked by restrained emotion and the frequent use of counterpoint, free from tensions or violence ,
3. — used as an intensive marked by deliberate effrontery or lack of due respect or discretion , facilitating or suggesting relief from heat ,
6. producing an impression of being cool, relatively lacking in timbre or resonance,
7. slang very good ; excellent , fashionable , hip , coolish adjective coolly also cooly adverb coolness noun Synonyms: see: cool
II. verb Date: before 12th century intransitive verb to become cool ; lose heat or warmth , to lose ardor or passion , transitive verb to make cool ; impart a feeling of coolness to ,
2. to moderate the heat, excitement, or force of ; calm , to slow or lessen the growth or activity of,
III. noun
Date: 15th century
a cool time, place, or situation ,
2. absence of excitement or emotional involvement ; detachment , poise , composure , hipness ,
IV. adverb
Date: 1841
in a casual and nonchalant manner