Name The Cat

Well it is the name of something black, and quite a lot get named this. But he also has an abbreviation shortened to three letters.
 
Another clue;

My first is in chaos but not in chaotic.
My next is in rythm and also Spasmodic.
My third is a round and kind of a circle,
My fourth is an angle and part of a buckle,
My fifth is in every and also eternal,
But the last is the end of all days which is nice,
And also a mystery as it appears twice.

:)
 
Rowan, I hope your clever clues will help someone far smarter than me to figure it out.
I am flummoxed.
 
Hint - There are two Y's in Mystery. ;)
 
I would love to try to figure this out but it is beyond me. Consider me your slow friend from Chicago.:)
 
I love a puzzle but this has me stumped.