Definition of southernize in US English:

southernize

(also southernise)

verb

  • 1Frequently with capital initial. To cause (a person or group of people) to adopt a character, style, outlook, etc., typical of the south of a country or region, especially the Southern states of the United States; to make southern in form or character.

  • 2To put (a text) into or amend (a linguistic form) according to a dialect characteristic of or predominant in the south. Chiefly with reference to southern Middle English.

Origin

Mid 19th century; earliest use found in John Young (1805–1881). From southern + -ize.