The only free and comprehensive online etymological dictionary of the Spanish language
último (Adjective) "last," "final"
15th cent. A learned borrowing from Latin ultimus 'id.,' which replaced a number of words for "last" in Old Spanish including cabero, çaguero, derradero, trasero, postrimero and postero. From Proto-Italic *ol-tamo 'id.,' from Proto-Indo-European *h2ol-tmHo- "furthest." From the root *h2el- "that" (see el (2), él). An ancient comparative with *h2ol-tero- "further" (whence ultra).
Portuguese último, Catalan últim, French ultime, Italian ultimo, Romanian ultim
Oscan últiumam "last"