boundary line between Pa
. & Md., regarded, before the Civil War, as separating the free states from the slave
states or, now
, the North from the South
: also Mason and Dixon's line
Webster’s New World College Dictionary, 4th Edition. Copyright © 2010 by
Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'Mason-Dixon Line'after C. Mason & J. Dixon, who surveyed it, 1763-67