"Cat" in slang means: female, person or friend. So, "Cool Cat" would just mean a cool person.
cool cat
Cool itself, unless you are using it to mean mildly cold, is a slang word. Just because it is old slang doesn't mean that it is not still slang.
Cool.
cat is under the table
It's an older slang with the same meaning as "cool" or "groovy."
It's slang for excellent or cool.
Steezy means cool. (Slang)
cool/chill
A calm mellow cat. Since you posted in idioms, I assume you mean the slang to describe a person. It means someone is hip, with-it, etc. Mostly used in jazz type clubs.
"50 slang" could refer to slang from the 1950s (such as "cool cat" or "greaser") or slang that originated in the area code 50 in Minnesota. More context would be needed to provide a specific answer.
The slang big cat often refers to the person in charge. It can also refer to someone who is dominant over others.
Cool meant awesome, in fashion, or popular.