the Mason-Dixon Line - definition and synonyms

 

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/ˌmeɪs(ə)n ˈdɪks(ə)n ˌlaɪn/
  1. the border between the two states of Maryland and Pennsylvania in the US that traditionally divides the north of the US from the south. In the past, this was the border between those southern states that supported slavery and the northern ones that did not.