n. (in the US) the boundary between Maryland and Pennsylvania, taken as the northern limit of the slave-owning States before the abolition of slavery.
[ C. Mason & J. Dixon, 18th-c. English astronomers who surveyed it ]
MASONDIXON LINE
Meaning of MASONDIXON LINE in English
Concise Oxford English dictionary. Краткий оксфордский словарь английского языка. 2012