Where does “tristíssimo” come from?

tristíssimo (Portuguese) comes from Portuguese Triste, from Old Occitan triste, from Latin trīstis, from Proto-Indo-European tristh₂s, from Proto-Indo-European steh₂- — to stand.

Ancestry of “tristíssimo”, step by step

Step	Language	Word	Meaning
1	Portuguese	Triste	sad; unhappy; down
2	Old Occitan	triste	—
3	Latin	trīstis	sad, unhappy, melancholy, morose
4	Proto-Indo-European	tristh₂s	a third party standing, after the two parties to...
5	Proto-Indo-European	steh₂-	to stand

Every word from Proto-Indo-European steh₂- →Every word from Proto-Indo-European tristh₂s →Every word from Latin trīstis →