The only free and comprehensive online etymological dictionary of the Spanish language
-ado Suffix Indicating likeness or relatedness.
From Latin -atus 'id.' From Proto-Italic *-ātos. From Proto-Indo-European *-eh2-tós 'id.' The first element *-eh2- is a thematic vowel; the second element *-tós is an adjective-forming suffix.
Indo-European
Romance
Asturian -áu, Portuguese -ado, Galician -ado, Catalan -at, French , Italian -ato, Romanian -at