fiesta

Fiesta comes straight from Spanish fiesta, which traces back to Late Latin festa, itself the plural form of festum, meaning "feast."

The facts don't describe a shift in meaning — the word seems to have carried the sense of celebration or feast-day from Latin through Spanish and into English largely intact.

It's a doublet of feast, fest, and fete — all descend from the same Latin root, just borrowed into English at different times and through different paths.