The definition of cool is slightly chilly, but not cold, or a slang term for popular or in style.
(adjective)See cool in Webster's New World College Dictionary
adjective
Origin: ME & OE col < IE base *gel-, cold, to freeze > chill, cold, L gelu
adverb
noun
intransitive verb
Origin: ME colien < OE colian, to cool
transitive verb
See cool in American Heritage Dictionary 4
adjective cool·er, cool·est
Origin:
Origin: Middle English cole
Origin: , from Old English cōl; see gel- in Indo-European roots
.Related Forms:
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