Something slightly more amazing than fantastic, but much more astounding than fantabulisticesqueastic! Basically, it's a cool way of saying that something is the greatest thing ever.
A word used to describe when you've had a fantastic, fabulous, fantastic day. This word falls under the category of closed compound words, and is typically used when you are too lazy to move your mouth around when you could do it with -3 times the effort.
White Chick: OMG. I just went to Starbucks and I had the most fantabulastic time!
White Chick 2: LOL. Really? What was it that made your time there so fantabulastic?
White Chick: OMG. I CAN'T EVEN. They just released the new Pumpkin Spice Latte! Totes my fave.