Where does “costosissimo” come from?

costosissimo (Italian) comes from Italian costoso, from Italian -oso, from Latin -ōsus, from Old Latin -ōssus.

Ancestry of “costosissimo”, step by step

StepLanguageWordMeaning
1Italiancostosocostly, expensive
2Italian-oso-ous, -ful, -y
3Latin-ōsusose, -ous, -ful (full of or overly prone to)
4Old Latin-ōssus—
Every word from Old Latin -ōssus →Every word from Latin -ōsus →Every word from Italian -oso →
costosissimo — Etymology, Origin & Word History | Etymology Explorer