What is the origin of the phrase "do a line with someone", meaning "have a regular romantic or sexual romantic relationship with someone"?
I learnt this phrase from an Irish colleague of mine the other day, but she did not know how the phrase originated.
Oxford dictionaries online say:
Definition of do a line with in English
(Irish and NZ, informal) have a regular romantic or sexual romantic relationship with (someone): "I knew if I went home for Christmas, I'd have to pretend I was doing a line with some man."