IPA: /fænˈtæstɪkli/
KK: /fæn'tæstɪkli/
In a way that is wonderful or amazing; to a great extent that seems unreal or imaginative.
The performance was fantastically entertaining, leaving the audience in awe.
Fantastically → It is formed from "fantastic" (from Latin *fantasticus*, meaning imaginative or fanciful) and the suffix "-ally" (meaning in a manner of). The word "fantastically" means in an imaginative or fanciful manner.
Think of something being done in an 'imaginative' way ('fantastic') — and the '-ally' just means in that manner. This helps you remember that 'fantastically' describes doing something in a very imaginative way.