Uncertain origin. Roberts assignsProto-Indo-European*wert- in the sense of turning the mouth to smile; De Vaan finds no credible Indo-European origin and rejects connections toSanskritव्रीडते(vrīḍate,“to be shy, bashful”).
^Williams, Edwin B. 1962.From Latin to Portuguese: Historical phonology and morphology of the Portuguese language. Philadelphia: University of Pennsylvania Press. Page 232.
Roberts, Edward A. (2014),A Comprehensive Etymological Dictionary of the Spanish Language with Families of Words based on Indo-European Roots, volume II, Xlibris Corporation,→ISBN
De Vaan, Michiel (2008),Etymological Dictionary of Latin and the other Italic Languages (Leiden Indo-European Etymological Dictionary Series; 7), Leiden, Boston: Brill,→ISBN,page522