cool

Ben Zimmer, who “sets the record straight on the ubiquitous” slang word cool, explains that its modern sense, “that is, in the ‘stylish’ or ‘admirable’ meaning popularized by the cool cats and chicks of the postwar era and exemplified by the all-purpose expression of appreciation or approval, ‘That’s cool’” has nothing to do with the word’s usage by writers and speakers from Abraham Lincoln to Zora Neale Hurston. He ends his investigation saying that “From our current vantage point, it’s easy to read older examples of cool as variations on the now-entrenched colloquial use. But for lovers of linguistic verisimilitude, that’s just uncool.”
As I learned from my students, all freshmen and clearly on top of colloquial “latter-day expressions,” cool is meanwhile totally uncool. What’s stylish or admirable now is chill, and one doesn’t stay cool anymore but chills it. Cool is just so 20th century, man!