Etymology: Middle English col, from Old English cōl; akin to Old High German kuoli cool, Old English ceald cold — more at cold
Date: before 12th century
1. moderately cold ; lacking in warmth
a. marked by steady dispassionate calmness and self-control <a cool and calculating administrator — Current Biography> b. lacking ardor or friendliness <a cool impersonal manner> c. of jazz marked by restrained emotion and the frequent use of counterpoint d. free from tensions or violence <meeting with minority groups in an attempt to keep the city cool> 3. — used as an intensive <a cool million dollars> 4. marked by deliberate effrontery or lack of due respect or discretion <a cool reply> 5. facilitating or suggesting relief from heat <a cool dress> 6. a. of a color producing an impression of being cool; specifically of a hue in the range violet through blue to green b. of a musical tone relatively lacking in timbre or resonance 7. slang a. very good ; excellent; also all right b. fashionable, hip <not happy with the new shoes…because they were not cool — Celestine Sibley> • coolish adjective • coolly also cooly adverb • coolness noun Synonyms: cool, composed, collected, unruffled, imperturbable, nonchalant mean free from agitation or excitement. cool may imply calmness, deliberateness, or dispassionateness <kept a cool head>. composed implies freedom from agitation as a result of self-discipline or a sedate disposition <the composed pianist gave a flawless concert>. collected implies a concentration of mind that eliminates distractions especially in moments of crisis <the nurse stayed calm and collected>. unruffled suggests apparent serenity and poise in the face of setbacks or in the midst of excitement <harried but unruffled>. imperturbable implies coolness or assurance even under severe provocation <the speaker remained imperturbable despite the heckling>. nonchalant stresses an easy coolness of manner or casualness that suggests indifference or unconcern <a nonchalant driver>. II. verb Date: before 12th century intransitive verb 1. to become cool ; lose heat or warmth <placed the pie in the window to cool> — sometimes used with off or down 2. to lose ardor or passion <his anger cooled> transitive verb 1. to make cool ; impart a feeling of coolness to <cooled the room with a fan> — often used with off or down <a swim cooled us off a little> 2. a. to moderate the heat, excitement, or force of ; calm <cooled her growing anger> b. to slow or lessen the growth or activity of — usually used with off or down <wants to cool off the economy without freezing it — Newsweek> III. noun Date: 15th century 1. a cool time, place, or situation <the cool of the evening> 2. a. absence of excitement or emotional involvement ; detachment <must surrender his fine cool and enter the closed crazy world of suicide — Wilfrid Sheed> b. poise, composure <press questions…seemed to rattle him and he lost his cool — New Republic> 3. hipness IV. adverb Date: 1841 in a casual and nonchalant manner <play it cool>
New Collegiate Dictionary. 2001.