The only free and comprehensive online etymological dictionary of the Spanish language
la f. (Definite Article) "the"
From Latin illa "that." Old Latin olla. From Proto-Italic *olna 'id.' From Proto-Indo-European *h2ol-na- "that." From the root *h2el- "that." See also ella.
Indo-European
Romance
Asturian la, Portuguese la, Catalan la, French la, Italian la, Romanian aia