Origin: Indo

PIE word *wasdʰos From black + a second element, possibly derived from one of the following: * From Irish fad (“length”), fada (“long”, adjective) (ultimately from Proto-Indo-European *wasdʰos (“long; wide”)) + dobhar (“moisture; sea; water”) (ultimately from Proto-Indo-European *dʰewbʰ- (“deep”)), referring to a long river. * From Old English ǣdre (“channel for liquids; river; (anatomy) artery or vein; sinew”), from Proto-Germanic *ēþrǭ (“rivulet; (anatomy) vein”), possibly from Proto-Indo-European *h₁éh₁t-r̥ ~ *h₁h₁t-éns (“lung; internal organ”), from *h₁eh₁t- (“breath; to breathe”) + *-r̥ (suffix forming nouns). However, this etymology has been doubted as it has been suggested that the long initial vowel in Old English would have been preserved in English and Scots. * From Proto-Brythonic *ador or *edir (“(possibly) name of a river”), possibly ultimately from Proto-Indo-European *hₐet- (“to go”) + *-r̥. The surname is from the river and the adjacent Blackadder House.

Etymology: Wiktionary (CC-BY-SA)