To make something less hot or to become less hot; can also mean to calm down or relax.
From Old English 'col,' related to German 'kühl' and Latin 'gelu' (frost); the word has meant 'of low temperature' for over a thousand years.
The word 'cool' meaning 'fashionable or excellent' is actually quite recent—it arose in jazz culture in the 1940s when musicians used 'cool' to mean calm and controlled, which then became a compliment for anything impressive.
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