Where does “gravíssimo” come from?

gravíssimo (Portuguese) comes from Portuguese grave, from Old Portuguese grave, from Latin gravis, from Proto-Indo-European gʷréh₂us, from Proto-Indo-European -us — Forms adjectives from Caland system roots.

Ancestry of “gravíssimo”, step by step

Step	Language	Word	Meaning
1	Portuguese	grave	serious; grave; low-pitched; grave; grave;...
2	Old Portuguese	grave	—
3	Latin	gravis	heavy; troublesome, hard; grave, serious
4	Proto-Indo-European	gʷréh₂us	heavy
5	Proto-Indo-European	-us	Forms adjectives from Caland system roots

Every word from Proto-Indo-European -us →Every word from Proto-Indo-European gʷréh₂us →Every word from Latin gravis →