The phrase אימתי קאתי מר in the Chassidic song is usually translated "When will the Master come?"
How exactly is the form קאתי derived? If I understand correctly, it must be a verbal form (whether Hebrew or Aramaic) but it does not seem to look like one. Can anyone please clarify what its root, binyan, tense, person / gender / number are? How is it vocalized? Does this word occur elsewhere in the mekorot or have any cognates, or any story behind it?
Note: it may well be that this question is off-topic for Mi Yodeya; apologies in this case - I could not find a better forum to ask it.