In parts of England 'a butty' is a word that means sandwich as in a bacon butty!

Similar to what the poster Mr. White mentioned, in Irish-English it is a way to indicate a friend or other times a sandwich.

I live in Wales in the UK and we're also known to call our close friends "butty's" too! Almost always used by men, I'm unsure whether it would be based on the sandwich but if you go to a pub in Wales you'll hear "He is my butty" "They were my buttys" "Listen to your butty" Etc.

Is it in the context of food? https://en.wikipedia.org/wiki/Chip_butty I love a good chip butty.