What is the meaning of the expression "come a calling"?
It's a very old-fashioned usage. It comes from an Old English prefix, on/an, meaning in, on, or at. So when you come a-calling, you are "in" or "at" the activity of calling.We find it in old expressions: He went a-hunting, let us go a-Maying (picking spring flowers), and so on.
The a- prefix also turns up, interestingly, in other words where we never notice it. My dictionary lists "aboard," "asleep," "agog," and "agoing." Amazing!
make terms: to come to terms; to make an agreement: to agree. 達成協議