Most slang words are coined to represent an age group or some kind of community for which outsiders don't know the slang word. As soon as those words go mainstream, they are out of fashion. It happens so fast that you can date a movie by the slang words it contains, or at least identify the period it's set in. But one slang word just refuses to go away- the word "cool," used for anything good in pretty much any way.
While the word itself goes back hundreds of years, it was first published as a slang word in 1884. That means it was being used as vocal slang for a long time before that. And it's still used today by all age groups. Besides that, it doesn't go out and in and out of fashion, but rather spreads further and becomes more common all the time. "Cool" can be mean many things besides temperature, but it's always a positive word. Linguist Dr. Erica Brozovsky goes through the history of "cool" and the many ways it's been used.
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