'blackguard' originates from Early Modern English, specifically the phrase 'black guard', where 'black' referred to being dirty or soiled and 'guard' referred to a group of attendants.

'black guard' changed from a two-word phrase referring to low-paid or dirty servants and attendants and eventually contracted into the single-word form 'blackguard', with its sense shifting to denote a dishonorable person.

Initially, it meant 'kitchen servants or a group of low attendants', but over time it evolved into its current primary meaning of 'a coarse, dishonorable person; scoundrel'.