The only free and comprehensive online etymological dictionary of the Spanish language
ex, ex- (Preposition, Prefix) "former," "out (of)"
From Latin ex 'id.' From Proto-Italic *eks 'id.' From Proto-Indo-European *h1éǵhs "out."
Indo-European
Romance
Asturian ex, Portuguese ex, Galician ex, Catalan ex, French ex, Italian ex, Romanian ex-
de Vaan, M. Etymological Dictionary of Latin and Other Italic Languages. BRILL. 2014.
Real Academia Española. Diccionario de la lengua española. Online. 23rd ed. Madrid: Espasa Calpa. 2014. http://www.rae.es/.
Sihler, A. New Comparative Grammar of Greek and Latin. Oxford University Press. 2008.