The only free and comprehensive online etymological dictionary of the Spanish language
-ero Noun-forming suffix indicating an occupation, agency or state of being.

From Latin -arius 'id.' From Proto-Italic *-ārio- 'id.' From Proto-Indo-European *-eh2-r-i̯o-

Romance: Western Vulgar Latin: Asturian -ariu, Portuguese -áriu, Galician -eiro, Catalan -er, French -ier, Italian -aio, Eastern Vulgar Latin: Aromanian -ar, Romanian -ar