Where does “fittissimo” come from?

fittissimo (Italian) comes from Italian fitto, from Vulgar Latin fictus, from Latin fissus, from Proto-Indo-European bʰidtós, from Proto-Indo-European bʰeyd-, from Proto-Indo-European bʰey- — bee.

Ancestry of “fittissimo”, step by step

Step	Language	Word	Meaning
1	Italian	fitto	past participle of figgere; thick; dense
2	Vulgar Latin	fictus	feigned, fictitious, false, counterfeit, having...
3	Latin	fissus	split, cloven
4	Proto-Indo-European	bʰidtós	split, cloven
5	Proto-Indo-European	bʰeyd-	to split
6	Proto-Indo-European	bʰey-	bee

Every word from Proto-Indo-European bʰey- →Every word from Proto-Indo-European bʰeyd- →Every word from Proto-Indo-European bʰidtós →