I assume I will have to accept this explanation, since it appears it is as 'concrete' as I'll ever get;
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" Aside from opposite to warm, it is a word used by youth that means about anything the user want's it mean.You and I, are too old to analyse it.
I'll be 69 in June, and we used the word often back when we were Young to give a thumbs up to someone. Cool was.....A D.T. Ducktail haircut, Black leather jacket, Engineer boots..... Chuck berry and Elvis were pretty cool also.Brenda Levy, a Cheerleader at my HS was really cool!
I bet you used the word cool back in the day, and really never stopped to analyse it."
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I have been guilty of a slip with the term "cool" when speaking with my 13 yr old grandaughter, but here again..that's with a 13 yr old and her teenage collloquialisms.
I'm just a bit older than you, NW..and I never did use that given term. However, I must confess my comparative term during my teenage years was "copacetic"..and I only had a vauge notion that it actually meant, "very satisfactory".
Since resorting to the "cool" would require a serious adult to put his maturity into a retrograde development, I am left wondering why some media sources consider a president being viewed as "cool", to be a plus factor among mature, voting age adults.