fabelhaft
fabulous
Exceptionally good, great, or wonderful. Used colloquially as a strong positive judgment.
Du siehst in diesem Kleid einfach fabelhaft aus!
You look simply fabulous in this dress!

fabulous / legendary
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fabulous
Exceptionally good, great, or wonderful. Used colloquially as a strong positive judgment.
Du siehst in diesem Kleid einfach fabelhaft aus!
You look simply fabulous in this dress!

The word is made up of 'Fabel' (fable) and the ending '-haft' (-like). The ending '-haft' means 'like' or 'in the manner of,' so 'fabelhaft' literally means 'as if from a fable.'
Die Kostüme im Theaterstück waren wirklich fabelhaft gestaltet.
The costumes in the play were designed in a truly fabulous way.
In the meaning 'großartig' (great), 'fabelhaft' is strong, often enthusiastic praise in colloquial language. It can have a slightly theatrical or very warm tone.
Wir hatten einen fabelhaften Abend im Restaurant.
We had a fabulous evening at the restaurant.
When it means 'großartig' (great), 'fabelhaft' is often used to describe people, experiences, or impressions: 'fabelhaft aussehen' (to look fabulous), 'ein fabelhafter Urlaub' (a fabulous vacation), or 'sich fabelhaft fühlen' (to feel fabulous).
Nach dem langen Schlaf fühle ich mich fabelhaft.
After the long sleep, I feel fabulous.
You can recognize the literal meaning 'sagenhaft' (legendary/mythical) from the context. It is almost only used in connection with myths, fairy tales, or fantasy, for example in 'fabelhafte Wesen' (mythical beings) or 'fabelhafte Welten' (mythical worlds).
Drachen und Einhörner sind fabelhafte Kreaturen aus alten Legenden.
Dragons and unicorns are mythical creatures from old legends.
bad
'schlecht' and 'fabelhaft' are opposites as evaluations. 'schlecht' expresses that something is not good or is disappointing. 'fabelhaft' is a strongly positive word and means great or wonderful. It often sounds a bit more emotional and enthusiastic than 'sehr gut' (very good). You use 'fabelhaft' especially when you want to clearly praise something.

Das Konzert heute Abend war fabelhaft.
The concert this evening was fabulous.
Am Montag war die Stimmung im Büro schlecht.
On Monday, the mood in the office was bad.