13th cent. Old Spanish passaro. From Vulgar Latin *passar 'id.' (Classical Latin passer "sparrow").
From Proto-Italic *pattro- 'id.' From Proto-Indo-European *pt-tro- "bird." From a root *pet- "to fly," with a possible (though tenuous) connection to pedir. This concise etymology is from Schrijver (1991), who proposes a reduction of the Proto-Italic nominative singular *pattros to a later *passr̥s and then finally passer.
Romance: Western Vulgar Latin: Asturian páxaru, Portuguese pássaro, Galician paxaro, French passereau, Italian passero ; Eastern Vulgar Latin: Romanian pasăre