Where does “grandissmo” come from?

grandissmo (Italian) comes from Latin grandissimus, from Latin grandis, from Proto-Italic *grandis.

Ancestry of “grandissmo”, step by step

Step	Language	Word	Meaning
1	Latin	grandissimus	superlative degree of grandis
2	Latin	grandis	full-grown, grown up; large, great, grand, lofty;...
3	Proto-Italic	*grandis	—

grandissmo — Etymology, Origin & Word History | Etymology Explorer