fett
fatty
Containing a high proportion of fat, especially in foods.
Die Soße ist mir zu fett, ich nehme lieber nur das Gemüse.
The sauce is too fatty for me; I'd rather just have the vegetables.

fat / bold
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fatty
Containing a high proportion of fat, especially in foods.
Die Soße ist mir zu fett, ich nehme lieber nur das Gemüse.
The sauce is too fatty for me; I'd rather just have the vegetables.

When 'fett' (fat) describes a person, it is very direct and is often felt to be insulting. It is stronger and more negative than the word 'dick' (overweight/fat).
Man sollte fremde Menschen nicht als fett bezeichnen.
You shouldn't describe strangers as fat.
The meaning 'großartig' (great) or 'toll' (cool) is typical of youth slang and very colloquial. In formal situations, you should avoid this usage.
Wow, dein neues Motorrad ist ja mega fett!
Wow, your new motorcycle is mega awesome!
In connection with texts, computers, or printing, 'fett' (bold) always means 'fettgedruckt' (boldface/bold). It is often used with verbs such as 'drucken' (to print), 'schreiben' (to write), or 'markieren' (to highlight/mark).
Bitte markieren Sie die wichtigen Stichwörter im Dokument fett.
Please mark the important keywords in the document in bold.
In the meaning 'großer Betrag' (large amount), 'fett' (big) is often used in combination with money, success, or profit. Typical expressions are 'ein fetter Gewinn' (a big profit), 'eine fette Beute' (a big haul), or 'ein fettes Gehalt' (a big salary).
Er hat mit dem Verkauf seiner Firma eine fette Summe kassiert.
He pocketed a big sum from selling his company.
The use of 'fett' (wasted) for 'stark betrunken' (very drunk) is very informal and belongs to colloquial language. You often hear it among friends.
Er konnte nicht mehr geradeaus laufen, so fett war er.
He couldn't walk straight anymore, he was that wasted.
When it comes to food, 'fett' (fatty) is often used to describe foods with a high fat content. Typical examples are 'fette Wurst' (fatty sausage), 'fetter Käse' (fatty cheese), or 'fettes Fleisch' (fatty meat).
Nach dem Sport esse ich lieber etwas Leichtes und keine fette Pizza.
After exercising, I'd rather eat something light and not a fatty pizza.
great / mad
'toll' and 'fett' can both express in colloquial language that something is very good or impressive. 'toll' is general and fits many situations. 'fett' in this meaning is much more casual and often sounds like youth slang or scene language. It is more likely to fit parties, music, successes, or strong impressions. Learners may confuse the words because both show enthusiasm. But 'fett' also has other meanings, for example with food or bodies. That is why 'toll' is safer if you simply want to speak positively.

Max findet den neuen Song richtig fett.
Max thinks the new song is really awesome.
Die Klassenfahrt nächste Woche wird bestimmt toll.
The class trip next week is sure to be great.