A large, non-venomous colubrid snake, Elaphe obsoleta, of eastern North America, with chiefly blackish coloration (also called pilot black-snake); specifically one of the subspecies E. o. obsoleta.
Origin
Late 19th century.
Definition of black rat snake in US English:
black rat snake
noun
A large, non-venomous colubrid snake, Elaphe obsoleta, of eastern North America, with chiefly blackish coloration (also called pilot black-snake); specifically one of the subspecies E. o. obsoleta.