mason and dixon's line

Century Dictionary and Cyclopedia

1. See line.

GNU Webster's 1913

1. n. the boundary line between Pennsylvania and Maryland, as run before the Revolution (1764-1767) by two English astronomers named Charles Mason and Jeremiah Dixon. In an extended sense, the line between the free and the slave States.

WordNet 3.0

1. n. the boundary between Maryland and Pennsylvania; symbolic dividing line between North and South before the American Civil War