The only free and comprehensive online etymological dictionary of the Spanish language
creíble (Adjective) "believable"
13th cent. From Latin credibilis 'id.,' from credere "to believe" (see creer).
Indo-European
Romance
Portuguese crível, credível, Catalan creïble, French crédible, Italian credibile, Romanian credibil
Celtic
Old Irish creitid "to believe," Middle Welsh credu 'id.,' Middle Breton crediff 'id.,' Cornish cresy 'id.'
Corominas, J. & J. Pascual. Diccionario crítico etimológico castellano e híspanico. 6 vols. Madrid: Gredos. 1991-1997.
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.