riesengroß
huge
Extremely large; of enormous or impressive proportions. It is an intensified form of 'groß' (big).
Die Freude über das Geschenk war riesengroß.
The joy over the gift was huge.

huge
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huge
Extremely large; of enormous or impressive proportions. It is an intensified form of 'groß' (big).
Die Freude über das Geschenk war riesengroß.
The joy over the gift was huge.

'Riesengroß' (huge) is a compound adjective made from 'der Riese' (giant) and 'groß' (big). It literally means 'as big as a giant' and is a figurative intensifier.
Vor uns stand ein riesengroßer Baum.
A huge tree stood in front of us.
Since 'riesengroß' (huge) is already an intensification of 'groß' (big), it is normally not compared. Forms like 'riesengrößer' or 'am riesengrößten' are uncommon.
Das Hochhaus war einfach riesengroß.
The high-rise was simply huge.
The adjective describes not only physical size, but also the intensity of feelings or abstract concepts. Typical phrases are 'riesengroße Freude' (huge joy), 'riesengroßer Hunger' (huge hunger), or 'riesengroßer Erfolg' (huge success).
Nach dem Sieg war die Erleichterung im Team riesengroß.
After the victory, the relief in the team was huge.
big / great
'groß' and 'riesengroß' both describe that something takes up a lot of space or has great extent. 'groß' is neutral and can be used for ordinary large things. 'riesengroß' is much stronger and means that something is extremely large or especially impressively large. The words can be confused because 'riesengroß' is built on 'groß'. But 'riesengroß' does not fit every normal large size; it is only used when you want to particularly emphasize the size.

Mein Kollege bringt morgen eine riesengroße Tasche mit ins Büro.
My colleague is bringing a huge bag to the office tomorrow.
Das Wohnzimmer ist groß genug für einen Esstisch und ein Sofa.
The living room is big enough for a dining table and a sofa.