'bailo' originates from Venetian (or Italian) 'bailo', ultimately from medieval Latin 'baiulus' (or related forms), where the root meant 'bearer' or 'custodian.'

'bailo' changed from medieval Latin/vernacular words such as 'baiulus' into Venetian/Italian 'bailo' and was adopted into English usage to denote the specific Venetian diplomatic office (especially the Constantinople post).

Initially, the root conveyed the sense of a 'bearer' or 'custodian,' but over time the term came to denote a particular official role: the Venetian resident representative or ambassador.