border village in Scotland, where, formerly, many eloping English couples went to be married: used figuratively of any similar village or town
See Gretna Green in American Heritage Dictionary 4
(grĕtˈnə)
A village of southern Scotland on the English border. It was famous as a place for runaway marriages from 1754 until 1856, when the Scottish law was changed to require a 21-day residence period for one of the parties before issuance of a license.