cool [OE] As early as the 1880s, cool, an Old English word related to *cold, was being used by black Americans to mean ‘excellent, pleasing’, and ‘stylish’. It only became more widely known when people started associating it with jazz musicians with a restrained and relaxed style in the 1940s. It then declined in popularity for a decade or two before regaining its position as the top all-purpose affirmative. Cool as a cucumber is also older than might be expected, going back to the mid 18th century.