Cool
The figurative, common usage of 'cool' as a general term of approbation is first attested from the late 19th century in Black American slang. Its usage became popular in the 1920s in American jazz circles. Since then its usage has spread all over the world wherever English is spoken. 'Cool' when followed by a quantity, usually money, as in 'a cool one hundred or thousand', dates from the late 1700s. Cool meaning lack of warmth as in a 'cool reception' or 'cooling' with regard to another person is even earlier and dates from the late 1600s. Other more literal uses of 'cool' meaning unflappable, as in a 'cool fish' or 'cool customer' date from the mid-19th century. 'Cool cat' was originally a jazz aficionado, and dates from the 1920s See also Chill/chill out.