What is the meaning of this conjunction?
"Ой-да, матушка... = " Ах-ты, матушка ( Ah, you, mother)
Only Ах is not Ah in English ("ah" is more like "А-а-а").
Where did you see it? Are you sure, it wasn't "ой, да."? That would mean something like "oh, yes", but I don't believe something like "ой-да" exists in Russian language.
It's from a song. The section goes like so (and this is straight from the lyric book):
Скрой седые заветы отцов
От глаза черного люта ворога
В гуще священных лесов."