You raise a really good point. Words like “neat” and “swell” left, but what’s so special about “cool”? I really have no idea. I use the word cool 3–4 times a day, sometimes more. I use the word the most when trying to get out of a conversation. For instance, a friend of mine refuses to shut up on the phone. The only thing I say in a two hour period is, “That’s cool,” in a monotone voice. She never gets the hint. Anyway, it might have something to do with the hippy movement. Since all parents of teenagers today were at least kids during the movement, and the hippys are still considered pretty cool (there I go!) today, maybe one of the words they used is still acceptable for that reason. (But then again, what happened to groovy?)