Adjective + issime

This suffix -issime comes from the Latin -issimus and means “the most”.

Génial means ‘great, fantastic’ and ‘génialissime’ means ‘the greatest’, ‘the most fantastic’, greatissime!

It is possible to make it with all adjectives but some are more common/
Simplissime (very easy)
Grandissime (very big)
Gravissime (very serious)
Rarissime (very rare)
Richissime (very rich)

Some nouns accept this suffix: Generalissime: generalissimo

And those that have an Italian origin are like -issimo:
Pianissimo
Fortissimo

We also have the word: bravissimo like in English!