Now and then the words "nifty" or "groovy" might drop into a conversation, instantly identifying the speaker as an old fogy or, worse, an old hippie.
But the word "cool" doesn't do that. "Cool" is constant. As a modifier, as the modified, as a noun and as a verb, "cool" has withstood the fleeting nature of most slang.
What is the reason for "cool's" longevity?