Seven swans a-swimming [duplicate]

In the famous Christmas carol "The Twelve Days of Christmas", presents like "geese a-laying" and "swans a-swimming" are mentioned. What does the "a" refer to in this context?


What does the "a" refer to in this context?

The a- is a prefix TFD used in a-laying and a-swimming

  1. literary or archaic (used before a present participle) in the act or process of: come a-running; go a-hunting etc...