adjective
huge
B1
riesig means huge or very large. It is a gradable adjective: comparative riesiger, superlative am riesigsten. Common antonym: winzig (tiny). It behaves like a regular adjective in inflection and can be used attributively or predicatively (ein riesiges Haus; das Haus ist riesig). Not a participle.
Examples
Als die Halle geöffnet wurde, zeigte sich, dass der Platz riesig war und viele Besucher hineinpassen konnten.
When the hall was opened, it became clear that the space was huge and many visitors could fit inside.
Das Hotel war riesig und hatte viele Zimmer.
The hotel was huge and had many rooms.
Details
Mnemonics
Picture a tiny house next to a giant one with a label 'riesig' on the big one.
Sounds a little like 'rice-y' — imagine something as big as a mountain of rice to recall 'huge'.
Notes
Riesig is a regular gradable adjective: use comparative and superlative forms for comparisons.