riesig
huge
Exceptionally large in dimensions, extent, or amount.
Das Unternehmen hat einen riesigen Gewinn gemacht.
The company made a huge profit.

huge
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huge
Exceptionally large in dimensions, extent, or amount.
Das Unternehmen hat einen riesigen Gewinn gemacht.
The company made a huge profit.

The adjective 'riesig' (huge) is derived from the noun 'der Riese' (a giant, a very large person in fairy tales). So it literally means 'like a giant' or 'gigantic'.
Vor dem Schloss stand eine riesige Eiche.
A huge oak tree stood in front of the castle.
In its literal meaning, 'riesig' (huge) is often combined with abstract or concrete nouns to emphasize their large extent. Common examples are: 'ein riesiger Erfolg' (a huge success), 'ein riesiges Problem' (a huge problem), 'eine riesige Menge' (a huge amount), or 'ein riesiger Unterschied' (a huge difference).
Der finanzielle Schaden durch den Sturm war riesig.
The financial damage caused by the storm was huge.
In colloquial speech, 'riesig' (huge/hugely) is often used like an adverb to intensify feelings or impressions. It then simply means 'very' or 'enormously'.
Wir hatten im Urlaub riesig Spaß.
We had huge fun on vacation.
very
'sehr' and 'riesig' can both make something stronger. 'sehr' is a general intensifier and works before many adjectives, adverbs, and also with some verbs. 'riesig' actually means exceptionally large. Colloquially, however, it can also be used like a strong intensifier, for example with joy. The words can be confused because 'riesig' sometimes works similarly to 'sehr'. Still, 'sehr' is more neutral and versatile, while 'riesig' sounds stronger, more figurative, and often colloquial.

Nach der Zusage war die Freude im Team riesig.
After the acceptance, the joy in the team was huge.
Sie hat sich sehr über die Einladung gefreut.
She was very happy about the invitation.